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2017-02-02fs: Better permission checking for submountsEric W. Biederman
To support unprivileged users mounting filesystems two permission checks have to be performed: a test to see if the user allowed to create a mount in the mount namespace, and a test to see if the user is allowed to access the specified filesystem. The automount case is special in that mounting the original filesystem grants permission to mount the sub-filesystems, to any user who happens to stumble across the their mountpoint and satisfies the ordinary filesystem permission checks. Attempting to handle the automount case by using override_creds almost works. It preserves the idea that permission to mount the original filesystem is permission to mount the sub-filesystem. Unfortunately using override_creds messes up the filesystems ordinary permission checks. Solve this by being explicit that a mount is a submount by introducing vfs_submount, and using it where appropriate. vfs_submount uses a new mount internal mount flags MS_SUBMOUNT, to let sget and friends know that a mount is a submount so they can take appropriate action. sget and sget_userns are modified to not perform any permission checks on submounts. follow_automount is modified to stop using override_creds as that has proven problemantic. do_mount is modified to always remove the new MS_SUBMOUNT flag so that we know userspace will never by able to specify it. autofs4 is modified to stop using current_real_cred that was put in there to handle the previous version of submount permission checking. cifs is modified to pass the mountpoint all of the way down to vfs_submount. debugfs is modified to pass the mountpoint all of the way down to trace_automount by adding a new parameter. To make this change easier a new typedef debugfs_automount_t is introduced to capture the type of the debugfs automount function. Cc: stable@vger.kernel.org Fixes: 069d5ac9ae0d ("autofs: Fix automounts by using current_real_cred()->uid") Fixes: aeaa4a79ff6a ("fs: Call d_automount with the filesystems creds") Reviewed-by: Trond Myklebust <trond.myklebust@primarydata.com> Reviewed-by: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2016-12-16Merge branch 'work.autofs' into for-linusAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-12-05namespace.c: constify struct path passed to a bunch of primitivesAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-12-03vfs: add path_is_mountpoint() helperIan Kent
d_mountpoint() can only be used reliably to establish if a dentry is not mounted in any namespace. It isn't aware of the possibility there may be multiple mounts using a given dentry that may be in a different namespace. Add helper functions, path_is_mountpoint(), that checks if a struct path is a mountpoint for this case. Link: http://lkml.kernel.org/r/20161011053358.27645.9729.stgit@pluto.themaw.net Signed-off-by: Ian Kent <raven@themaw.net> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Omar Sandoval <osandov@osandov.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-09-30mnt: Add a per mount namespace limit on the number of mountsEric W. Biederman
CAI Qian <caiqian@redhat.com> pointed out that the semantics of shared subtrees make it possible to create an exponentially increasing number of mounts in a mount namespace. mkdir /tmp/1 /tmp/2 mount --make-rshared / for i in $(seq 1 20) ; do mount --bind /tmp/1 /tmp/2 ; done Will create create 2^20 or 1048576 mounts, which is a practical problem as some people have managed to hit this by accident. As such CVE-2016-6213 was assigned. Ian Kent <raven@themaw.net> described the situation for autofs users as follows: > The number of mounts for direct mount maps is usually not very large because of > the way they are implemented, large direct mount maps can have performance > problems. There can be anywhere from a few (likely case a few hundred) to less > than 10000, plus mounts that have been triggered and not yet expired. > > Indirect mounts have one autofs mount at the root plus the number of mounts that > have been triggered and not yet expired. > > The number of autofs indirect map entries can range from a few to the common > case of several thousand and in rare cases up to between 30000 and 50000. I've > not heard of people with maps larger than 50000 entries. > > The larger the number of map entries the greater the possibility for a large > number of active mounts so it's not hard to expect cases of a 1000 or somewhat > more active mounts. So I am setting the default number of mounts allowed per mount namespace at 100,000. This is more than enough for any use case I know of, but small enough to quickly stop an exponential increase in mounts. Which should be perfect to catch misconfigurations and malfunctioning programs. For anyone who needs a higher limit this can be changed by writing to the new /proc/sys/fs/mount-max sysctl. Tested-by: CAI Qian <caiqian@redhat.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2016-06-24fs: Treat foreign mounts as nosuidAndy Lutomirski
If a process gets access to a mount from a different user namespace, that process should not be able to take advantage of setuid files or selinux entrypoints from that filesystem. Prevent this by treating mounts from other mount namespaces and those not owned by current_user_ns() or an ancestor as nosuid. This will make it safer to allow more complex filesystems to be mounted in non-root user namespaces. This does not remove the need for MNT_LOCK_NOSUID. The setuid, setgid, and file capability bits can no longer be abused if code in a user namespace were to clear nosuid on an untrusted filesystem, but this patch, by itself, is insufficient to protect the system from abuse of files that, when execed, would increase MAC privilege. As a more concrete explanation, any task that can manipulate a vfsmount associated with a given user namespace already has capabilities in that namespace and all of its descendents. If they can cause a malicious setuid, setgid, or file-caps executable to appear in that mount, then that executable will only allow them to elevate privileges in exactly the set of namespaces in which they are already privileges. On the other hand, if they can cause a malicious executable to appear with a dangerous MAC label, running it could change the caller's security context in a way that should not have been possible, even inside the namespace in which the task is confined. As a hardening measure, this would have made CVE-2014-5207 much more difficult to exploit. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2015-04-18Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace Pull usernamespace mount fixes from Eric Biederman: "Way back in October Andrey Vagin reported that umount(MNT_DETACH) could be used to defeat MNT_LOCKED. As I worked to fix this I discovered that combined with mount propagation and an appropriate selection of shared subtrees a reference to a directory on an unmounted filesystem is not necessary. That MNT_DETACH is allowed in user namespace in a form that can break MNT_LOCKED comes from my early misunderstanding what MNT_DETACH does. To avoid breaking existing userspace the conflict between MNT_DETACH and MNT_LOCKED is fixed by leaving mounts that are locked to their parents in the mount hash table until the last reference goes away. While investigating this issue I also found an issue with __detach_mounts. The code was unnecessarily and incorrectly triggering mount propagation. Resulting in too many mounts going away when a directory is deleted, and too many cpu cycles are burned while doing that. Looking some more I realized that __detach_mounts by only keeping mounts connected that were MNT_LOCKED it had the potential to still leak information so I tweaked the code to keep everything locked together that possibly could be. This code was almost ready last cycle but Al invented fs_pin which slightly simplifies this code but required rewrites and retesting, and I have not been in top form for a while so it took me a while to get all of that done. Similiarly this pull request is late because I have been feeling absolutely miserable all week. The issue of being able to escape a bind mount has not yet been addressed, as the fixes are not yet mature" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: mnt: Update detach_mounts to leave mounts connected mnt: Fix the error check in __detach_mounts mnt: Honor MNT_LOCKED when detaching mounts fs_pin: Allow for the possibility that m_list or s_list go unused. mnt: Factor umount_mnt from umount_tree mnt: Factor out unhash_mnt from detach_mnt and umount_tree mnt: Fail collect_mounts when applied to unmounted mounts mnt: Don't propagate unmounts to locked mounts mnt: On an unmount propagate clearing of MNT_LOCKED mnt: Delay removal from the mount hash. mnt: Add MNT_UMOUNT flag mnt: In umount_tree reuse mnt_list instead of mnt_hash mnt: Don't propagate umounts in __detach_mounts mnt: Improve the umount_tree flags mnt: Use hlist_move_list in namespace_unlock
2015-04-15init: export name_to_dev_t and mark name argument as constDan Ehrenberg
DM will switch its device lookup code to using name_to_dev_t() so it must be exported. Also, the @name argument should be marked const. Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2015-04-02mnt: Add MNT_UMOUNT flagEric W. Biederman
In some instances it is necessary to know if the the unmounting process has begun on a mount. Add MNT_UMOUNT to make that reliably testable. This fix gets used in fixing locked mounts in MNT_DETACH Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2014-10-24vfs: introduce clone_private_mount()Miklos Szeredi
Overlayfs needs a private clone of the mount, so create a function for this and export to modules. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
2014-08-11Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull vfs updates from Al Viro: "Stuff in here: - acct.c fixes and general rework of mnt_pin mechanism. That allows to go for delayed-mntput stuff, which will permit mntput() on deep stack without worrying about stack overflows - fs shutdown will happen on shallow stack. IOW, we can do Eric's umount-on-rmdir series without introducing tons of stack overflows on new mntput() call chains it introduces. - Bruce's d_splice_alias() patches - more Miklos' rename() stuff. - a couple of regression fixes (stable fodder, in the end of branch) and a fix for API idiocy in iov_iter.c. There definitely will be another pile, maybe even two. I'd like to get Eric's series in this time, but even if we miss it, it'll go right in the beginning of for-next in the next cycle - the tricky part of prereqs is in this pile" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (40 commits) fix copy_tree() regression __generic_file_write_iter(): fix handling of sync error after DIO switch iov_iter_get_pages() to passing maximal number of pages fs: mark __d_obtain_alias static dcache: d_splice_alias should detect loops exportfs: update Exporting documentation dcache: d_find_alias needn't recheck IS_ROOT && DCACHE_DISCONNECTED dcache: remove unused d_find_alias parameter dcache: d_obtain_alias callers don't all want DISCONNECTED dcache: d_splice_alias should ignore DCACHE_DISCONNECTED dcache: d_splice_alias mustn't create directory aliases dcache: close d_move race in d_splice_alias dcache: move d_splice_alias namei: trivial fix to vfs_rename_dir comment VFS: allow ->d_manage() to declare -EISDIR in rcu_walk mode. cifs: support RENAME_NOREPLACE hostfs: support rename flags shmem: support RENAME_EXCHANGE shmem: support RENAME_NOREPLACE btrfs: add RENAME_NOREPLACE ...
2014-08-07death to mnt_pinnedAl Viro
Rather than playing silly buggers with vfsmount refcounts, just have acct_on() ask fs/namespace.c for internal clone of file->f_path.mnt and replace it with said clone. Then attach the pin to original vfsmount. Voila - the clone will be alive until the file gets closed, making sure that underlying superblock remains active, etc., and we can drop the original vfsmount, so that it's not kept busy. If the file lives until the final mntput of the original vfsmount, we'll notice that there's an fs_pin (one in bsd_acct_struct that holds that file) and mnt_pin_kill() will take it out. Since ->kill() is synchronous, we won't proceed past that point until these files are closed (and private clones of our vfsmount are gone), so we get the same ordering warranties we used to get. mnt_pin()/mnt_unpin()/->mnt_pinned is gone now, and good riddance - it never became usable outside of kernel/acct.c (and racy wrt umount even there). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2014-07-31mnt: Correct permission checks in do_remountEric W. Biederman
While invesgiating the issue where in "mount --bind -oremount,ro ..." would result in later "mount --bind -oremount,rw" succeeding even if the mount started off locked I realized that there are several additional mount flags that should be locked and are not. In particular MNT_NOSUID, MNT_NODEV, MNT_NOEXEC, and the atime flags in addition to MNT_READONLY should all be locked. These flags are all per superblock, can all be changed with MS_BIND, and should not be changable if set by a more privileged user. The following additions to the current logic are added in this patch. - nosuid may not be clearable by a less privileged user. - nodev may not be clearable by a less privielged user. - noexec may not be clearable by a less privileged user. - atime flags may not be changeable by a less privileged user. The logic with atime is that always setting atime on access is a global policy and backup software and auditing software could break if atime bits are not updated (when they are configured to be updated), and serious performance degradation could result (DOS attack) if atime updates happen when they have been explicitly disabled. Therefore an unprivileged user should not be able to mess with the atime bits set by a more privileged user. The additional restrictions are implemented with the addition of MNT_LOCK_NOSUID, MNT_LOCK_NODEV, MNT_LOCK_NOEXEC, and MNT_LOCK_ATIME mnt flags. Taken together these changes and the fixes for MNT_LOCK_READONLY should make it safe for an unprivileged user to create a user namespace and to call "mount --bind -o remount,... ..." without the danger of mount flags being changed maliciously. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2014-07-31mnt: Only change user settable mount flags in remountEric W. Biederman
Kenton Varda <kenton@sandstorm.io> discovered that by remounting a read-only bind mount read-only in a user namespace the MNT_LOCK_READONLY bit would be cleared, allowing an unprivileged user to the remount a read-only mount read-write. Correct this by replacing the mask of mount flags to preserve with a mask of mount flags that may be changed, and preserve all others. This ensures that any future bugs with this mask and remount will fail in an easy to detect way where new mount flags simply won't change. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2014-04-01smarter propagate_mnt()Al Viro
The current mainline has copies propagated to *all* nodes, then tears down the copies we made for nodes that do not contain counterparts of the desired mountpoint. That sets the right propagation graph for the copies (at teardown time we move the slaves of removed node to a surviving peer or directly to master), but we end up paying a fairly steep price in useless allocations. It's fairly easy to create a situation where N calls of mount(2) create exactly N bindings, with O(N^2) vfsmounts allocated and freed in process. Fortunately, it is possible to avoid those allocations/freeings. The trick is to create copies in the right order and find which one would've eventually become a master with the current algorithm. It turns out to be possible in O(nodes getting propagation) time and with no extra allocations at all. One part is that we need to make sure that eventual master will be created before its slaves, so we need to walk the propagation tree in a different order - by peer groups. And iterate through the peers before dealing with the next group. Another thing is finding the (earlier) copy that will be a master of one we are about to create; to do that we are (temporary) marking the masters of mountpoints we are attaching the copies to. Either we are in a peer of the last mountpoint we'd dealt with, or we have the following situation: we are attaching to mountpoint M, the last copy S_0 had been attached to M_0 and there are sequences S_0...S_n, M_0...M_n such that S_{i+1} is a master of S_{i}, S_{i} mounted on M{i} and we need to create a slave of the first S_{k} such that M is getting propagation from M_{k}. It means that the master of M_{k} will be among the sequence of masters of M. On the other hand, the nearest marked node in that sequence will either be the master of M_{k} or the master of M_{k-1} (the latter - in the case if M_{k-1} is a slave of something M gets propagation from, but in a wrong peer group). So we go through the sequence of masters of M until we find a marked one (P). Let N be the one before it. Then we go through the sequence of masters of S_0 until we find one (say, S) mounted on a node D that has P as master and check if D is a peer of N. If it is, S will be the master of new copy, if not - the master of S will be. That's it for the hard part; the rest is fairly simple. Iterator is in next_group(), handling of one prospective mountpoint is propagate_one(). It seems to survive all tests and gives a noticably better performance than the current mainline for setups that are seriously using shared subtrees. Cc: stable@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-11-09RCU'd vfsmountsAl Viro
* RCU-delayed freeing of vfsmounts * vfsmount_lock replaced with a seqlock (mount_lock) * sequence number from mount_lock is stored in nameidata->m_seq and used when we exit RCU mode * new vfsmount flag - MNT_SYNC_UMOUNT. Set by umount_tree() when its caller knows that vfsmount will have no surviving references. * synchronize_rcu() done between unlocking namespace_sem in namespace_unlock() and doing pending mntput(). * new helper: legitimize_mnt(mnt, seq). Checks the mount_lock sequence number against seq, then grabs reference to mnt. Then it rechecks mount_lock again to close the race and either returns success or drops the reference it has acquired. The subtle point is that in case of MNT_SYNC_UMOUNT we can simply decrement the refcount and sod off - aforementioned synchronize_rcu() makes sure that final mntput() won't come until we leave RCU mode. We need that, since we don't want to end up with some lazy pathwalk racing with umount() and stealing the final mntput() from it - caller of umount() may expect it to return only once the fs is shut down and we don't want to break that. In other cases (i.e. with MNT_SYNC_UMOUNT absent) we have to do full-blown mntput() in case of mount_lock sequence number mismatch happening just as we'd grabbed the reference, but in those cases we won't be stealing the final mntput() from anything that would care. * mntput_no_expire() doesn't lock anything on the fast path now. Incidentally, SMP and UP cases are handled the same way - no ifdefs there. * normal pathname resolution does *not* do any writes to mount_lock. It does, of course, bump the refcounts of vfsmount and dentry in the very end, but that's it. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-07-24vfs: Lock in place mounts from more privileged usersEric W. Biederman
When creating a less privileged mount namespace or propogating mounts from a more privileged to a less privileged mount namespace lock the submounts so they may not be unmounted individually in the child mount namespace revealing what is under them. This enforces the reasonable expectation that it is not possible to see under a mount point. Most of the time mounts are on empty directories and revealing that does not matter, however I have seen an occassionaly sloppy configuration where there were interesting things concealed under a mount point that probably should not be revealed. Expirable submounts are not locked because they will eventually unmount automatically so whatever is under them already needs to be safe for unprivileged users to access. From a practical standpoint these restrictions do not appear to be significant for unprivileged users of the mount namespace. Recursive bind mounts and pivot_root continues to work, and mounts that are created in a mount namespace may be unmounted there. All of which means that the common idiom of keeping a directory of interesting files and using pivot_root to throw everything else away continues to work just fine. Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Acked-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2013-03-27vfs: Add a mount flag to lock read only bind mountsEric W. Biederman
When a read-only bind mount is copied from mount namespace in a higher privileged user namespace to a mount namespace in a lesser privileged user namespace, it should not be possible to remove the the read-only restriction. Add a MNT_LOCK_READONLY mount flag to indicate that a mount must remain read-only. CC: stable@vger.kernel.org Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2012-01-03vfs: move fsnotify junk to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: move mnt_devnameAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: move mnt_list to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: move the rest of int fields to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: mnt_id/mnt_group_id movedAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: mnt_ns moved to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: take mnt_share/mnt_slave/mnt_slave_list and mnt_expire to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: take mnt_master to struct mountAl Viro
make IS_MNT_SLAVE take struct mount * at the same time Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: take mnt_child/mnt_mounts to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: all counters taken to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: move mnt_mountpoint to struct mountAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: mnt_parent moved to struct mountAl Viro
the second victim... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: the first spoils - mnt_hash movedAl Viro
taken out of struct vfsmount into struct mount Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: mnt_drop_write_file()Al Viro
new helper (wrapper around mnt_drop_write()) to be used in pair with mnt_want_write_file(). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-03vfs: make do_kern_mount() staticAl Viro
the only user outside of fs/namespace.c has died Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-07-26atomic: use <linux/atomic.h>Arun Sharma
This allows us to move duplicated code in <asm/atomic.h> (atomic_inc_not_zero() for now) to <linux/atomic.h> Signed-off-by: Arun Sharma <asharma@fb.com> Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: David Miller <davem@davemloft.net> Cc: Eric Dumazet <eric.dumazet@gmail.com> Acked-by: Mike Frysinger <vapier@gentoo.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-16sanitize vfsmount refcounting changesAl Viro
Instead of splitting refcount between (per-cpu) mnt_count and (SMP-only) mnt_longrefs, make all references contribute to mnt_count again and keep track of how many are longterm ones. Accounting rules for longterm count: * 1 for each fs_struct.root.mnt * 1 for each fs_struct.pwd.mnt * 1 for having non-NULL ->mnt_ns * decrement to 0 happens only under vfsmount lock exclusive That allows nice common case for mntput() - since we can't drop the final reference until after mnt_longterm has reached 0 due to the rules above, mntput() can grab vfsmount lock shared and check mnt_longterm. If it turns out to be non-zero (which is the common case), we know that this is not the final mntput() and can just blindly decrement percpu mnt_count. Otherwise we grab vfsmount lock exclusive and do usual decrement-and-check of percpu mnt_count. For fs_struct.c we have mnt_make_longterm() and mnt_make_shortterm(); namespace.c uses the latter in places where we don't already hold vfsmount lock exclusive and opencodes a few remaining spots where we need to manipulate mnt_longterm. Note that we mostly revert the code outside of fs/namespace.c back to what we used to have; in particular, normal code doesn't need to care about two kinds of references, etc. And we get to keep the optimization Nick's variant had bought us... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-01-15Unexport do_add_mount() and add in follow_automount(), not ->d_automount()David Howells
Unexport do_add_mount() and make ->d_automount() return the vfsmount to be added rather than calling do_add_mount() itself. follow_automount() will then do the addition. This slightly complicates things as ->d_automount() normally wants to add the new vfsmount to an expiration list and start an expiration timer. The problem with that is that the vfsmount will be deleted if it has a refcount of 1 and the timer will not repeat if the expiration list is empty. To this end, we require the vfsmount to be returned from d_automount() with a refcount of (at least) 2. One of these refs will be dropped unconditionally. In addition, follow_automount() must get a 3rd ref around the call to do_add_mount() lest it eat a ref and return an error, leaving the mount we have open to being expired as we would otherwise have only 1 ref on it. d_automount() should also add the the vfsmount to the expiration list (by calling mnt_set_expiry()) and start the expiration timer before returning, if this mechanism is to be used. The vfsmount will be unlinked from the expiration list by follow_automount() if do_add_mount() fails. This patch also fixes the call to do_add_mount() for AFS to propagate the mount flags from the parent vfsmount. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-01-07fs: scale mntget/mntputNick Piggin
The problem that this patch aims to fix is vfsmount refcounting scalability. We need to take a reference on the vfsmount for every successful path lookup, which often go to the same mount point. The fundamental difficulty is that a "simple" reference count can never be made scalable, because any time a reference is dropped, we must check whether that was the last reference. To do that requires communication with all other CPUs that may have taken a reference count. We can make refcounts more scalable in a couple of ways, involving keeping distributed counters, and checking for the global-zero condition less frequently. - check the global sum once every interval (this will delay zero detection for some interval, so it's probably a showstopper for vfsmounts). - keep a local count and only taking the global sum when local reaches 0 (this is difficult for vfsmounts, because we can't hold preempt off for the life of a reference, so a counter would need to be per-thread or tied strongly to a particular CPU which requires more locking). - keep a local difference of increments and decrements, which allows us to sum the total difference and hence find the refcount when summing all CPUs. Then, keep a single integer "long" refcount for slow and long lasting references, and only take the global sum of local counters when the long refcount is 0. This last scheme is what I implemented here. Attached mounts and process root and working directory references are "long" references, and everything else is a short reference. This allows scalable vfsmount references during path walking over mounted subtrees and unattached (lazy umounted) mounts with processes still running in them. This results in one fewer atomic op in the fastpath: mntget is now just a per-CPU inc, rather than an atomic inc; and mntput just requires a spinlock and non-atomic decrement in the common case. However code is otherwise bigger and heavier, so single threaded performance is basically a wash. Signed-off-by: Nick Piggin <npiggin@kernel.dk>
2010-08-11vfs: remove unused MNT_STRICTATIMEMiklos Szeredi
Commit d0adde574b8487ef30f69e2d08bba769e4be513f added MNT_STRICTATIME but it isn't actually used (MS_STRICTATIME clears MNT_RELATIME and MNT_NOATIME rather than setting any mount flag). Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2010-07-28fsnotify/vfsmount: add fsnotify fields to struct vfsmountAndreas Gruenbacher
This patch adds the list and mask fields needed to support vfsmount marks. These are the same fields fsnotify needs on an inode. They are not used, just declared and we note where the cleanup hook should be (the function is not yet defined) Signed-off-by: Andreas Gruenbacher <agruen@suse.de> Signed-off-by: Eric Paris <eparis@redhat.com>
2010-03-04Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6 * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6: (52 commits) init: Open /dev/console from rootfs mqueue: fix typo "failues" -> "failures" mqueue: only set error codes if they are really necessary mqueue: simplify do_open() error handling mqueue: apply mathematics distributivity on mq_bytes calculation mqueue: remove unneeded info->messages initialization mqueue: fix mq_open() file descriptor leak on user-space processes fix race in d_splice_alias() set S_DEAD on unlink() and non-directory rename() victims vfs: add NOFOLLOW flag to umount(2) get rid of ->mnt_parent in tomoyo/realpath hppfs can use existing proc_mnt, no need for do_kern_mount() in there Mirror MS_KERNMOUNT in ->mnt_flags get rid of useless vfsmount_lock use in put_mnt_ns() Take vfsmount_lock to fs/internal.h get rid of insanity with namespace roots in tomoyo take check for new events in namespace (guts of mounts_poll()) to namespace.c Don't mess with generic_permission() under ->d_lock in hpfs sanitize const/signedness for udf nilfs: sanitize const/signedness in dealing with ->d_name.name ... Fix up fairly trivial (famous last words...) conflicts in drivers/infiniband/core/uverbs_main.c and security/tomoyo/realpath.c
2010-03-03Mirror MS_KERNMOUNT in ->mnt_flagsAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2010-03-03Take vfsmount_lock to fs/internal.hAl Viro
no more users left outside of fs/*.c (and very few outside of fs/namespace.c, actually) Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2010-03-03VFS: Clean up shared mount flag propagationValerie Aurora
The handling of mount flags in set_mnt_shared() got a little tangled up during previous cleanups, with the following problems: * MNT_PNODE_MASK is defined as a literal constant when it should be a bitwise xor of other MNT_* flags * set_mnt_shared() clears and then sets MNT_SHARED (part of MNT_PNODE_MASK) * MNT_PNODE_MASK could use a comment in mount.h * MNT_PNODE_MASK is a terrible name, change to MNT_SHARED_MASK This patch fixes these problems. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2010-02-17percpu: add __percpu sparse annotations to fsTejun Heo
Add __percpu sparse annotations to fs. These annotations are to make sparse consider percpu variables to be in a different address space and warn if accessed without going through percpu accessors. This patch doesn't affect normal builds. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: Alex Elder <aelder@sgi.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
2009-06-11fs: introduce mnt_clone_writenpiggin@suse.de
This patch speeds up lmbench lat_mmap test by about another 2% after the first patch. Before: avg = 462.286 std = 5.46106 After: avg = 453.12 std = 9.58257 (50 runs of each, stddev gives a reasonable confidence) It does this by introducing mnt_clone_write, which avoids some heavyweight operations of mnt_want_write if called on a vfsmount which we know already has a write count; and mnt_want_write_file, which can call mnt_clone_write if the file is open for write. After these two patches, mnt_want_write and mnt_drop_write go from 7% on the profile down to 1.3% (including mnt_clone_write). [AV: mnt_want_write_file() should take file alone and derive mnt from it; not only all callers have that form, but that's the only mnt about which we know that it's already held for write if file is opened for write] Cc: Dave Hansen <haveblue@us.ibm.com> Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2009-06-11fs: mnt_want_write speedupnpiggin@suse.de
This patch speeds up lmbench lat_mmap test by about 8%. lat_mmap is set up basically to mmap a 64MB file on tmpfs, fault in its pages, then unmap it. A microbenchmark yes, but it exercises some important paths in the mm. Before: avg = 501.9 std = 14.7773 After: avg = 462.286 std = 5.46106 (50 runs of each, stddev gives a reasonable confidence, but there is quite a bit of variation there still) It does this by removing the complex per-cpu locking and counter-cache and replaces it with a percpu counter in struct vfsmount. This makes the code much simpler, and avoids spinlocks (although the msync is still pretty costly, unfortunately). It results in about 900 bytes smaller code too. It does increase the size of a vfsmount, however. It should also give a speedup on large systems if CPUs are frequently operating on different mounts (because the existing scheme has to operate on an atomic in the struct vfsmount when switching between mounts). But I'm most interested in the single threaded path performance for the moment. [AV: minor cleanup] Cc: Dave Hansen <haveblue@us.ibm.com> Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2009-03-26Add a strictatime mount optionMatthew Garrett
Add support for explicitly requesting full atime updates. This makes it possible for kernels to default to relatime but still allow userspace to override it. Signed-off-by: Matthew Garrett <mjg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-10-16include/linux/mount.h: remove CVS keywordAdrian Bunk
Remove a CVS keyword that wasn't updated for a long time from a comment. Signed-off-by: Adrian Bunk <bunk@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-08-01[PATCH] pass struct path * to do_add_mount()Al Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2008-07-26[PATCH] vfs: use kstrdup() and check failing allocationLi Zefan
- use kstrdup() instead of kmalloc() + memcpy() - return NULL if allocating ->mnt_devname failed - mnt_devname should be const Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: Cyrill Gorcunov <gorcunov@gmail.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>