[PATCH] ceph: avoid putting the realm twice when docoding snaps fails

[xiubli@redhat.com]

From: Xiubo Li <xiubli@redhat.com>

When decoding the snaps fails it maybe leaving the 'first_realm'
and 'realm' pointing to the same snaprealm memory. And then it'll
put it twice and could cause random use-after-free, BUG_ON, etc
issues.

Cc: stable@vger.kernel.org
URL: https://tracker.ceph.com/issues/57686
Signed-off-by: Xiubo Li <xiubli@redhat.com>
---
 fs/ceph/snap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 9bceed2ebda3..baf17df05107 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -849,10 +849,12 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
 	if (realm_to_rebuild && p >= e)
 		rebuild_snap_realms(realm_to_rebuild, &dirty_realms);
 
-	if (!first_realm)
+	if (!first_realm) {
 		first_realm = realm;
-	else
+		realm = NULL;
+	} else {
 		ceph_put_snap_realm(mdsc, realm);
+	}
 
 	if (p < e)
 		goto more;
-- 
2.31.1