quota: Fix possible oops in __dquot_initialize()

When quotaon(8) races with __dquot_initialize() or dqget() fails because
of EIO, ENOSPC, or similar error, we could possibly dereference NULL pointer
in inode->i_dquot[cnt]. Add proper checking.

Reported-by: Dmitry Monakhov <dmonakhov@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 1bc38f56fa7c..0fed41e6efcd 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -1386,6 +1386,9 @@ static void __dquot_initialize(struct inode *inode, int type)
                 /* Avoid races with quotaoff() */
                 if (!sb_has_quota_active(sb, cnt))
                         continue;
+                /* We could race with quotaon or dqget() could have failed */
+                if (!got[cnt])
+                        continue;
                 if (!inode->i_dquot[cnt]) {
                         inode->i_dquot[cnt] = got[cnt];
                         got[cnt] = NULL;