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From:   Vasily Averin <vvs@virtuozzo.com>
Subject: [PATCH] ipc/util.c: sysvipc_find_ipc() incorrectly updates position
 index
To:     linux-kernel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Waiman Long <longman@redhat.com>,
        Andreas Schwab <schwab@suse.de>
References: <ad24ee52-21a8-3ff0-e968-63d315472b91@virtuozzo.com>
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Date:   Wed, 6 May 2020 09:25:54 +0300
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new_pos should jump through hole of unused ids,
pos can be updated inside "for" cycle.

Cc: stable@vger.kernel.org
Fixes: 89163f93c6f9 ("ipc/util.c: sysvipc_find_ipc() should increase position index")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 ipc/util.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/ipc/util.c b/ipc/util.c
index 7acccfd..cfa0045 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -764,21 +764,21 @@ static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
 			total++;
 	}
 
-	*new_pos = pos + 1;
+	ipc = NULL;
 	if (total >= ids->in_use)
-		return NULL;
+		goto out;
 
 	for (; pos < ipc_mni; pos++) {
 		ipc = idr_find(&ids->ipcs_idr, pos);
 		if (ipc != NULL) {
 			rcu_read_lock();
 			ipc_lock_object(ipc);
-			return ipc;
+			break;
 		}
 	}
-
-	/* Out of range - return NULL to terminate iteration */
-	return NULL;
+out:
+	*new_pos = pos + 1;
+	return ipc;
 }
 
 static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
-- 
1.8.3.1