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


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