From 9da3f2b74054406f87dff7101a569217ffceb29b Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Tue, 28 Aug 2018 22:14:20 +0200 Subject: x86/fault: BUG() when uaccess helpers fault on kernel addresses There have been multiple kernel vulnerabilities that permitted userspace to pass completely unchecked pointers through to userspace accessors: - the waitid() bug - commit 96ca579a1ecc ("waitid(): Add missing access_ok() checks") - the sg/bsg read/write APIs - the infiniband read/write APIs These don't happen all that often, but when they do happen, it is hard to test for them properly; and it is probably also hard to discover them with fuzzing. Even when an unmapped kernel address is supplied to such buggy code, it just returns -EFAULT instead of doing a proper BUG() or at least WARN(). Try to make such misbehaving code a bit more visible by refusing to do a fixup in the pagefault handler code when a userspace accessor causes a #PF on a kernel address and the current context isn't whitelisted. Signed-off-by: Jann Horn Signed-off-by: Thomas Gleixner Tested-by: Kees Cook Cc: Andy Lutomirski Cc: kernel-hardening@lists.openwall.com Cc: dvyukov@google.com Cc: Masami Hiramatsu Cc: "Naveen N. Rao" Cc: Anil S Keshavamurthy Cc: "David S. Miller" Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Cc: Borislav Petkov Link: https://lkml.kernel.org/r/20180828201421.157735-7-jannh@google.com --- fs/namespace.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs/namespace.c') diff --git a/fs/namespace.c b/fs/namespace.c index 99186556f8d3..d86830c86ce8 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2642,6 +2642,7 @@ static long exact_copy_from_user(void *to, const void __user * from, if (!access_ok(VERIFY_READ, from, n)) return n; + current->kernel_uaccess_faults_ok++; while (n) { if (__get_user(c, f)) { memset(t, 0, n); @@ -2651,6 +2652,7 @@ static long exact_copy_from_user(void *to, const void __user * from, f++; n--; } + current->kernel_uaccess_faults_ok--; return n; } -- cgit v1.2.3