[PATCH] r/o bind mounts: make access() use new r/o helper

It is OK to let access() go without using a mnt_want/drop_write() pair because it doesn't actually do writes to the filesystem, and it is inherently racy anyway. This is a rare case when it is OK to use __mnt_is_readonly() directly. Acked-by: Al Viro <[email protected]> Signed-off-by: Christoph Hellwig <[email protected]> Signed-off-by: Dave Hansen <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Al Viro <[email protected]>
blinkosm · Apr 19, 2008 · 2f676cb · 2f676cb
1 parent 9ac9b84
commit 2f676cb
Showing 1 changed file with 11 additions and 2 deletions.
diff --git a/fs/open.c b/fs/open.c
@@ -459,8 +459,17 @@ asmlinkage long sys_faccessat(int dfd, const char __user *filename, int mode)
 	if(res || !(mode & S_IWOTH) ||
 	   special_file(nd.path.dentry->d_inode->i_mode))
 		goto out_path_release;
-
-	if(IS_RDONLY(nd.path.dentry->d_inode))
+	/*
+	 * This is a rare case where using __mnt_is_readonly()
+	 * is OK without a mnt_want/drop_write() pair.  Since
+	 * no actual write to the fs is performed here, we do
+	 * not need to telegraph to that to anyone.
+	 *
+	 * By doing this, we accept that this access is
+	 * inherently racy and know that the fs may change
+	 * state before we even see this result.
+	 */
+	if (__mnt_is_readonly(nd.path.mnt))
 		res = -EROFS;
 
 out_path_release: