inotify: fix locking around inotify watching in the idr
The are races around the idr storage of inotify watches. It's possible
that a watch could be found from sys_inotify_rm_watch() in the idr, but it
could be removed from the idr before that code does it's removal. Move the
locking and the refcnt'ing so that these have to happen atomically.
Signed-off-by: Eric Paris <eparis@redhat.com>
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index d8f73c2..ce1f582 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -364,20 +364,53 @@
return error;
}
+/*
+ * Remove the mark from the idr (if present) and drop the reference
+ * on the mark because it was in the idr.
+ */
static void inotify_remove_from_idr(struct fsnotify_group *group,
struct inotify_inode_mark_entry *ientry)
{
struct idr *idr;
+ struct fsnotify_mark_entry *entry;
+ struct inotify_inode_mark_entry *found_ientry;
+ int wd;
spin_lock(&group->inotify_data.idr_lock);
idr = &group->inotify_data.idr;
- idr_remove(idr, ientry->wd);
- spin_unlock(&group->inotify_data.idr_lock);
+ wd = ientry->wd;
+
+ if (wd == -1)
+ goto out;
+
+ entry = idr_find(&group->inotify_data.idr, wd);
+ if (unlikely(!entry))
+ goto out;
+
+ found_ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry);
+ if (unlikely(found_ientry != ientry)) {
+ /* We found an entry in the idr with the right wd, but it's
+ * not the entry we were told to remove. eparis seriously
+ * fucked up somewhere. */
+ WARN_ON(1);
+ ientry->wd = -1;
+ goto out;
+ }
+
+ /* One ref for being in the idr, one ref held by the caller */
+ BUG_ON(atomic_read(&entry->refcnt) < 2);
+
+ idr_remove(idr, wd);
ientry->wd = -1;
+
+ /* removed from the idr, drop that ref */
+ fsnotify_put_mark(entry);
+out:
+ spin_unlock(&group->inotify_data.idr_lock);
}
+
/*
- * Send IN_IGNORED for this wd, remove this wd from the idr, and drop the
- * internal reference help on the mark because it is in the idr.
+ * Send IN_IGNORED for this wd, remove this wd from the idr.
*/
void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry,
struct fsnotify_group *group)
@@ -417,9 +450,6 @@
/* remove this entry from the idr */
inotify_remove_from_idr(group, ientry);
- /* removed from idr, drop that reference */
- fsnotify_put_mark(entry);
-
atomic_dec(&group->inotify_data.user->inotify_watches);
}
@@ -535,6 +565,9 @@
goto out_err;
}
+ /* we put the mark on the idr, take a reference */
+ fsnotify_get_mark(&tmp_ientry->fsn_entry);
+
/* we are on the idr, now get on the inode */
ret = fsnotify_add_mark(&tmp_ientry->fsn_entry, group, inode);
if (ret) {
@@ -543,9 +576,6 @@
goto out_err;
}
- /* we put the mark on the idr, take a reference */
- fsnotify_get_mark(&tmp_ientry->fsn_entry);
-
/* update the idr hint, who cares about races, it's just a hint */
group->inotify_data.last_wd = tmp_ientry->wd;