xattr: handle idmapped mounts

When interacting with extended attributes the vfs verifies that the
caller is privileged over the inode with which the extended attribute is
associated. For posix access and posix default extended attributes a uid
or gid can be stored on-disk. Let the functions handle posix extended
attributes on idmapped mounts. If the inode is accessed through an
idmapped mount we need to map it according to the mount's user
namespace. Afterwards the checks are identical to non-idmapped mounts.
This has no effect for e.g. security xattrs since they don't store uids
or gids and don't perform permission checks on them like posix acls do.

Link: https://lore.kernel.org/r/20210121131959.646623-10-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Tycho Andersen <tycho@tycho.pizza>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

5 files changed, 20 insertions, 17 deletions

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 3e9957ae19fa..f81b836c2256 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -85,9 +85,9 @@ int ovl_copy_xattr(struct super_block *sb, struct dentry *old,
 		if (ovl_is_private_xattr(sb, name))
 			continue;
 retry:
-		size = vfs_getxattr(old, name, value, value_size);
+		size = vfs_getxattr(&init_user_ns, old, name, value, value_size);
 		if (size == -ERANGE)
-			size = vfs_getxattr(old, name, NULL, 0);
+			size = vfs_getxattr(&init_user_ns, old, name, NULL, 0);
 
 		if (size < 0) {
 			error = size;
@@ -114,7 +114,7 @@ retry:
 			error = 0;
 			continue; /* Discard */
 		}
-		error = vfs_setxattr(new, name, value, size, 0);
+		error = vfs_setxattr(&init_user_ns, new, name, value, size, 0);
 		if (error) {
 			if (error != -EOPNOTSUPP || ovl_must_copy_xattr(name))
 				break;
@@ -795,7 +795,7 @@ static ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value)
 	ssize_t res;
 	char *buf;
 
-	res = vfs_getxattr(dentry, name, NULL, 0);
+	res = vfs_getxattr(&init_user_ns, dentry, name, NULL, 0);
 	if (res == -ENODATA || res == -EOPNOTSUPP)
 		res = 0;
 
@@ -804,7 +804,7 @@ static ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value)
 		if (!buf)
 			return -ENOMEM;
 
-		res = vfs_getxattr(dentry, name, buf, res);
+		res = vfs_getxattr(&init_user_ns, dentry, name, buf, res);
 		if (res < 0)
 			kfree(buf);
 		else
@@ -846,8 +846,8 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
 	 * don't want that to happen for normal copy-up operation.
 	 */
 	if (capability) {
-		err = vfs_setxattr(upperpath.dentry, XATTR_NAME_CAPS,
-				   capability, cap_size, 0);
+		err = vfs_setxattr(&init_user_ns, upperpath.dentry,
+				   XATTR_NAME_CAPS, capability, cap_size, 0);
 		if (err)
 			goto out_free;
 	}
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 29840820a46c..d75c96cb18c3 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -449,7 +449,7 @@ static int ovl_set_upper_acl(struct dentry *upperdentry, const char *name,
 	if (err < 0)
 		goto out_free;
 
-	err = vfs_setxattr(upperdentry, name, buffer, size, XATTR_CREATE);
+	err = vfs_setxattr(&init_user_ns, upperdentry, name, buffer, size, XATTR_CREATE);
 out_free:
 	kfree(buffer);
 	return err;
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 5aa66881dbd7..023fde466e3a 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -352,7 +352,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 		goto out;
 
 	if (!value && !upperdentry) {
-		err = vfs_getxattr(realdentry, name, NULL, 0);
+		err = vfs_getxattr(&init_user_ns, realdentry, name, NULL, 0);
 		if (err < 0)
 			goto out_drop_write;
 	}
@@ -367,10 +367,11 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	if (value)
-		err = vfs_setxattr(realdentry, name, value, size, flags);
+		err = vfs_setxattr(&init_user_ns, realdentry, name, value, size,
+				   flags);
 	else {
 		WARN_ON(flags != XATTR_REPLACE);
-		err = vfs_removexattr(realdentry, name);
+		err = vfs_removexattr(&init_user_ns, realdentry, name);
 	}
 	revert_creds(old_cred);
 
@@ -392,7 +393,7 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 		ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry);
 
 	old_cred = ovl_override_creds(dentry->d_sb);
-	res = vfs_getxattr(realdentry, name, value, size);
+	res = vfs_getxattr(&init_user_ns, realdentry, name, value, size);
 	revert_creds(old_cred);
 	return res;
 }
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index b487e48c7fd4..0002834f664a 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -186,7 +186,7 @@ static inline ssize_t ovl_do_getxattr(struct ovl_fs *ofs, struct dentry *dentry,
 				      size_t size)
 {
 	const char *name = ovl_xattr(ofs, ox);
-	return vfs_getxattr(dentry, name, value, size);
+	return vfs_getxattr(&init_user_ns, dentry, name, value, size);
 }
 
 static inline int ovl_do_setxattr(struct ovl_fs *ofs, struct dentry *dentry,
@@ -194,7 +194,7 @@ static inline int ovl_do_setxattr(struct ovl_fs *ofs, struct dentry *dentry,
 				  size_t size)
 {
 	const char *name = ovl_xattr(ofs, ox);
-	int err = vfs_setxattr(dentry, name, value, size, 0);
+	int err = vfs_setxattr(&init_user_ns, dentry, name, value, size, 0);
 	pr_debug("setxattr(%pd2, \"%s\", \"%*pE\", %zu, 0) = %i\n",
 		 dentry, name, min((int)size, 48), value, size, err);
 	return err;
@@ -204,7 +204,7 @@ static inline int ovl_do_removexattr(struct ovl_fs *ofs, struct dentry *dentry,
 				     enum ovl_xattr ox)
 {
 	const char *name = ovl_xattr(ofs, ox);
-	int err = vfs_removexattr(dentry, name);
+	int err = vfs_removexattr(&init_user_ns, dentry, name);
 	pr_debug("removexattr(%pd2, \"%s\") = %i\n", dentry, name, err);
 	return err;
 }
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index e24c995c5fd4..8168ab2dda11 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -794,11 +794,13 @@ retry:
 		 * allowed as upper are limited to "normal" ones, where checking
 		 * for the above two errors is sufficient.
 		 */
-		err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_DEFAULT);
+		err = vfs_removexattr(&init_user_ns, work,
+				      XATTR_NAME_POSIX_ACL_DEFAULT);
 		if (err && err != -ENODATA && err != -EOPNOTSUPP)
 			goto out_dput;
 
-		err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_ACCESS);
+		err = vfs_removexattr(&init_user_ns, work,
+				      XATTR_NAME_POSIX_ACL_ACCESS);
 		if (err && err != -ENODATA && err != -EOPNOTSUPP)
 			goto out_dput;