lkml.org 
[lkml]   [2007]   [Apr]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [NETLINK] Don't attach callback to a going-away netlink socket
    Evgeniy Polyakov wrote:
    > On Wed, Apr 18, 2007 at 12:16:18PM +0400, Pavel Emelianov (xemul@sw.ru) wrote:
    >
    >>Sorry, I forgot to put netdev and David in Cc when I first sent it.
    >>
    >>There is a race between netlink_dump_start() and netlink_release()
    >>that can lead to the situation when a netlink socket with non-zero
    >>callback is freed.
    >
    >
    > Out of curiosity, why not to fix a netlink_dump_start() to remove
    > callback in error path, since in 'no-error' path it removes it in
    > netlink_dump().


    It already does (netlink_destroy_callback), but that doesn't help
    with this race though since without this patch we don't enter the
    error path.

    > And, btw, can release method be called while socket is being used, I
    > thought about proper reference counters should prevent this, but not
    > 100% sure with RCU dereferencing of the descriptor.


    The problem is asynchronous processing of the dump request in the
    context of a different process. Process requests a dump, message
    is queued and process returns from sendmsg since some other process
    is already processing the queue. Then the process closes the socket,
    resulting in netlink_release being called. When the dump request
    is finally processed the race Pavel described might happen. This
    can only happen for netlink families that use mutex_try_lock for
    queue processing of course.

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-04-18 10:29    [W:4.317 / U:0.796 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site