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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Vasily Averin <vvs@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Waiman Long <longman@redhat.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Manfred Spraul <manfred@colorfullife.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Ingo Molnar <mingo@redhat.com>, NeilBrown <neilb@suse.com>,
        Peter Oberparleiter <oberpar@linux.ibm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 026/168] ipc/util.c: sysvipc_find_ipc() should increase position index
Date:   Tue, 28 Apr 2020 20:23:20 +0200
Message-Id: <20200428182235.022176918@linuxfoundation.org>
In-Reply-To: <20200428182231.704304409@linuxfoundation.org>
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From: Vasily Averin <vvs@virtuozzo.com>

[ Upstream commit 89163f93c6f969da5811af5377cc10173583123b ]

If seq_file .next function does not change position index, read after
some lseek can generate unexpected output.

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: NeilBrown <neilb@suse.com>
Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/b7a20945-e315-8bb0-21e6-3875c14a8494@virtuozzo.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 ipc/util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ipc/util.c b/ipc/util.c
index d126d156efc64..594871610d454 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -764,13 +764,13 @@ static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
 			total++;
 	}
 
+	*new_pos = pos + 1;
 	if (total >= ids->in_use)
 		return NULL;
 
 	for (; pos < ipc_mni; pos++) {
 		ipc = idr_find(&ids->ipcs_idr, pos);
 		if (ipc != NULL) {
-			*new_pos = pos + 1;
 			rcu_read_lock();
 			ipc_lock_object(ipc);
 			return ipc;
-- 
2.20.1