[PATCH 5.6 069/194] ipc/util.c: sysvipc_find_ipc() incorrectly updates position index

Greg Kroah-Hartman
2020-05-18T18:13:04Z

From: Vasily Averin <vvs@virtuozzo.com>

[ Upstream commit 5e698222c70257d13ae0816720dde57c56f81e15 ]

Commit 89163f93c6f9 ("ipc/util.c: sysvipc_find_ipc() should increase
position index") is causing this bug (seen on 5.6.8):

# ipcs -q

------ Message Queues --------
key msqid owner perms used-bytes messages

# ipcmk -Q
Message queue id: 0
# ipcs -q

------ Message Queues --------
key msqid owner perms used-bytes messages
0x82db8127 0 root 644 0 0

# ipcmk -Q
Message queue id: 1
# ipcs -q

------ Message Queues --------
key msqid owner perms used-bytes messages
0x82db8127 0 root 644 0 0
0x76d1fb2a 1 root 644 0 0

# ipcrm -q 0
# ipcs -q

------ Message Queues --------
key msqid owner perms used-bytes messages
0x76d1fb2a 1 root 644 0 0
0x76d1fb2a 1 root 644 0 0

# ipcmk -Q
Message queue id: 2
# ipcrm -q 2
# ipcs -q

------ Message Queues --------
key msqid owner perms used-bytes messages
0x76d1fb2a 1 root 644 0 0
0x76d1fb2a 1 root 644 0 0

# ipcmk -Q
Message queue id: 3
# ipcrm -q 1
# ipcs -q

------ Message Queues --------
key msqid owner perms used-bytes messages
0x7c982867 3 root 644 0 0
0x7c982867 3 root 644 0 0
0x7c982867 3 root 644 0 0
0x7c982867 3 root 644 0 0

Whenever an IPC item with a low id is deleted, the items with higher ids
are duplicated, as if filling a hole.

new_pos should jump through hole of unused ids, pos can be updated
inside "for" cycle.

Fixes: 89163f93c6f9 ("ipc/util.c: sysvipc_find_ipc() should increase position index")
Reported-by: Andreas Schwab <schwab@suse.de>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
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: NeilBrown <neilb@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/4921fe9b-9385-a2b4-1dc4-1099be6d2e39@virtuozzo.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
ipc/util.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/ipc/util.c b/ipc/util.c
index 2d70f25f64b83..c4a67982ec008 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)
--
2.20.1