Messages in this thread Patch in this message | | | Date | Tue, 7 Aug 2007 13:45:58 -0700 | From | Greg KH <> | Subject | [2.6.22.2 review 37/84] Fix user struct leakage with locked IPC shem segment |
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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/
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