lkml.org 
[lkml]   [2007]   [Aug]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[2.6.22.2 review 37/84] Fix user struct leakage with locked IPC shem segment

    From: Pavel Emelianov <xemul@openvz.org>

    When user locks an ipc shmem segmant with SHM_LOCK ctl and the segment is
    already locked the shmem_lock() function returns 0. After this the
    subsequent code leaks the existing user struct:

    == ipc/shm.c: sys_shmctl() ==
    ...
    err = shmem_lock(shp->shm_file, 1, user);
    if (!err) {
    shp->shm_perm.mode |= SHM_LOCKED;
    shp->mlock_user = user;
    }
    ...
    ==

    Other results of this are:
    1. the new shp->mlock_user is not get-ed and will point to freed
    memory when the task dies.
    2. the RLIMIT_MEMLOCK is screwed on both user structs.

    The exploit looks like this:

    ==
    id = shmget(...);
    setresuid(uid, 0, 0);
    shmctl(id, SHM_LOCK, NULL);
    setresuid(uid + 1, 0, 0);
    shmctl(id, SHM_LOCK, NULL);
    ==

    My solution is to return 0 to the userspace and do not change the
    segment's user.

    Signed-off-by: Pavel Emelianov <xemul@openvz.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    ipc/shm.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/ipc/shm.c
    +++ b/ipc/shm.c
    @@ -716,7 +716,7 @@ asmlinkage long sys_shmctl (int shmid, i
    struct user_struct * user = current->user;
    if (!is_file_hugepages(shp->shm_file)) {
    err = shmem_lock(shp->shm_file, 1, user);
    - if (!err) {
    + if (!err && !(shp->shm_perm.mode & SHM_LOCKED)){
    shp->shm_perm.mode |= SHM_LOCKED;
    shp->mlock_user = user;
    }
    --
    -
    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: 2007-08-07 23:11    [W:4.061 / U:0.096 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site