inotify: fix race (d599e36a) · Commits · 戴 / test

There is a race between setting an inode's children's "parent watched" flag when placing the first watch on a parent, and instantiating new children of that parent: a child could miss having its flags set by set_dentry_child_flags, but then inotify_d_instantiate might still see !inotify_inode_watched. The solution is to set_dentry_child_flags after adding the watch. Locking is taken care of, because both set_dentry_child_flags and inotify_d_instantiate hold dcache_lock and child->d_locks. Signed-off-by:

Nick Piggin <npiggin@suse.de> Cc: Robert Love <rlove@google.com> Cc: John McCutchan <ttb@tentacle.dhs.org> Cc: Jan Kara <jack@ucw.cz> Cc: Yan Zheng <yanzheng@21cn.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/inotify.c

+10 −3

Original line number	Diff line number	Diff line
		@@ -627,6 +627,7 @@ s32 inotify_add_watch(struct inotify_handle ih, struct inotify_watch watch,
		struct inode *inode, u32 mask)
		{
		int ret = 0;
		int newly_watched;

		/* don't allow invalid bits: we don't want flags set */
		mask &= IN_ALL_EVENTS \| IN_ONESHOT;
		@@ -653,12 +654,18 @@ s32 inotify_add_watch(struct inotify_handle ih, struct inotify_watch watch,
		*/
		watch->inode = igrab(inode);

		if (!inotify_inode_watched(inode))
		set_dentry_child_flags(inode, 1);

		/* Add the watch to the handle's and the inode's list */
		newly_watched = !inotify_inode_watched(inode);
		list_add(&watch->h_list, &ih->watches);
		list_add(&watch->i_list, &inode->inotify_watches);
		/*
		* Set child flags _after_ adding the watch, so there is no race
		* windows where newly instantiated children could miss their parent's
		* watched flag.
		*/
		if (newly_watched)
		set_dentry_child_flags(inode, 1);

		out:
		mutex_unlock(&ih->mutex);
		mutex_unlock(&inode->inotify_mutex);

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