fsnotify: check if file is actually being watched for pre-content events on open

So far, we set FMODE_NONOTIFY_ flags at open time if we know that there
are no permission event watchers at all on the filesystem, but lack of
FMODE_NONOTIFY_ flags does not mean that the file is actually watched.

For pre-content events, it is possible to optimize things so that we
don't bother trying to send pre-content events if file was not watched
(through sb, mnt, parent or inode itself) on open. Set FMODE_NONOTIFY_
flags according to that.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/2ddcc9f8d1fde48d085318a6b5a889289d8871d8.1731684329.git.josef@toxicpanda.com

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 569ec356e4cef1bea87d380efbc86630e3c230c1..9e483fface1e5d37f3c472d3c01a9b172be5feb4 100644 (file)
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -193,7 +193,7 @@ static bool fsnotify_event_needs_parent(struct inode *inode, __u32 mnt_mask,
        return mask & marks_mask;
 }
 
-/* Are there any inode/mount/sb objects that are interested in this event? */
+/* Are there any inode/mount/sb objects that watch for these events? */
 static inline bool fsnotify_object_watched(struct inode *inode, __u32 mnt_mask,
                                           __u32 mask)
 {
@@ -632,7 +632,9 @@ EXPORT_SYMBOL_GPL(fsnotify);
  */
 void file_set_fsnotify_mode(struct file *file)
 {
-       struct super_block *sb = file->f_path.dentry->d_sb;
+       struct dentry *dentry = file->f_path.dentry, *parent;
+       struct super_block *sb = dentry->d_sb;
+       __u32 mnt_mask, p_mask;
 
        /* Is it a file opened by fanotify? */
        if (FMODE_FSNOTIFY_NONE(file->f_mode))
@@ -653,11 +655,32 @@ void file_set_fsnotify_mode(struct file *file)
         * If there are permission event watchers but no pre-content event
         * watchers, set FMODE_NONOTIFY | FMODE_NONOTIFY_PERM to indicate that.
         */
-       if (likely(!fsnotify_sb_has_priority_watchers(sb,
+       if ((!d_is_dir(dentry) && !d_is_reg(dentry)) ||
+           likely(!fsnotify_sb_has_priority_watchers(sb,
                                                FSNOTIFY_PRIO_PRE_CONTENT))) {
                file->f_mode |= FMODE_NONOTIFY | FMODE_NONOTIFY_PERM;
                return;
        }
+
+       /*
+        * OK, there are some pre-content watchers. Check if anybody is
+        * watching for pre-content events on *this* file.
+        */
+       mnt_mask = READ_ONCE(real_mount(file->f_path.mnt)->mnt_fsnotify_mask);
+       if (unlikely(fsnotify_object_watched(d_inode(dentry), mnt_mask,
+                                    FSNOTIFY_PRE_CONTENT_EVENTS)))
+               return;
+
+       /* Is parent watching for pre-content events on this file? */
+       if (dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED) {
+               parent = dget_parent(dentry);
+               p_mask = fsnotify_inode_watches_children(d_inode(parent));
+               dput(parent);
+               if (p_mask & FSNOTIFY_PRE_CONTENT_EVENTS)
+                       return;
+       }
+       /* Nobody watching for pre-content events from this file */
+       file->f_mode |= FMODE_NONOTIFY | FMODE_NONOTIFY_PERM;
 }
 #endif
 

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 3ecf7768e577940f9ea79393c38bc2550ce7ddb8..9c105244815d420d9788a4b70fd129a1e24ce20d 100644 (file)
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -77,6 +77,9 @@
  */
 #define ALL_FSNOTIFY_DIRENT_EVENTS (FS_CREATE | FS_DELETE | FS_MOVE | FS_RENAME)
 
+/* Pre-content events can be used to fill file content */
+#define FSNOTIFY_PRE_CONTENT_EVENTS 0
+
 #define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM | \
                                  FS_OPEN_EXEC_PERM)