Messages in this thread | | | Date | Mon, 16 Jul 2007 15:17:38 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Fix user struct leakage with locked IPC shem segment |
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On Mon, 16 Jul 2007 16:24:12 +0400 Pavel Emelianov <xemul@openvz.org> 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, people@openvz.org have discovered (and fixed) an ongoing stream of obscure but serious and quite long-standing bugs.
How are you discovering these bugs?
> == 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?
> 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> > > --- > > --- ./ipc/shm.c.shlfix 2007-07-06 10:58:57.000000000 +0400 > +++ ./ipc/shm.c 2007-07-16 16:12:34.000000000 +0400 > @@ -715,7 +715,7 @@ 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/
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