[PATCH] inotify: fix watch count leak when fsnotify_add_inode_mark_locked() fails

[Chia-Ming Chang <chiamingc@synology.com>]

When fsnotify_add_inode_mark_locked() fails in inotify_new_watch(),
the error path calls inotify_remove_from_idr() but does not call
dec_inotify_watches() to undo the preceding inc_inotify_watches().
This leaks a watch count, and repeated failures can exhaust the
max_user_watches limit with -ENOSPC even when no watches are active.

Prior to commit 1cce1eea0aff ("inotify: Convert to using per-namespace
limits"), the watch count was incremented after fsnotify_add_mark_locked()
succeeded, so this path was not affected. The conversion moved
inc_inotify_watches() before the mark insertion without adding the
corresponding rollback.

Add the missing dec_inotify_watches() call in the error path.

Fixes: 1cce1eea0aff ("inotify: Convert to using per-namespace limits")
Cc: stable@vger.kernel.org
Signed-off-by: Chia-Ming Chang <chiamingc@synology.com>
Signed-off-by: robbieko <robbieko@synology.com>
---
 fs/notify/inotify/inotify_user.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index b372fb2c56bd..0d813c52ff9c 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -621,6 +621,7 @@ static int inotify_new_watch(struct fsnotify_group *group,
 	if (ret) {
 		/* we failed to get on the inode, get off the idr */
 		inotify_remove_from_idr(group, tmp_i_mark);
+		dec_inotify_watches(group->inotify_data.ucounts);
 		goto out_err;
 	}
 
-- 
2.34.1


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