[lkml]   [2007]   [Jul]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [Devel] Re: [PATCH] Fix user struct leakage with locked IPC shem segment
Andrew Morton wrote:
> On Mon, 16 Jul 2007 16:24:12 +0400
> Pavel Emelianov <> wrote:
>>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:
> I'm curious. For the past few months, have discovered
> (and fixed) an ongoing stream of obscure but serious and quite
> long-standing bugs.

thanks a lot :@)

> How are you discovering these bugs?

Not sure what to answer :) Just trying to do our best.

This bug was thought over by Pavel for about 3 month after a single
uid leak in container was detected by beancounters' kernel memory accounting...

>>== 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.
> That sounds fairly serious - can this lead to memory corruption and crashes?

Yes it can. According to Pavel when the shmem segment is destroyed it
puts the mlock_user pointer, which can already be stalled.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-07-17 11:09    [W:0.048 / U:13.700 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site