[PATCH] ocfs2: fix use-after-free when unmounting read-only filesystem

[Luís Henriques]

It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
fstest generic/452.  After mounting a filesystem as read-only, quotas are
suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
unmounting the filesystem, an UAF access to the oinfo will eventually cause a
crash.

Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
---
 fs/ocfs2/super.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index 0b0e6a132101..988d1c076861 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -952,8 +952,10 @@ static void ocfs2_disable_quotas(struct ocfs2_super *osb)
 	for (type = 0; type < OCFS2_MAXQUOTAS; type++) {
 		if (!sb_has_quota_loaded(sb, type))
 			continue;
-		oinfo = sb_dqinfo(sb, type)->dqi_priv;
-		cancel_delayed_work_sync(&oinfo->dqi_sync_work);
+		if (!sb_has_quota_suspended(sb, type)) {
+			oinfo = sb_dqinfo(sb, type)->dqi_priv;
+			cancel_delayed_work_sync(&oinfo->dqi_sync_work);
+		}
 		inode = igrab(sb->s_dquot.files[type]);
 		/* Turn off quotas. This will remove all dquot structures from
 		 * memory and so they will be automatically synced to global