[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <469B636C.3060007@openvz.org>
Date: Mon, 16 Jul 2007 16:24:12 +0400
From: Pavel Emelianov <xemul@...nvz.org>
To: Andrew Morton <akpm@...l.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC: devel@...nvz.org
Subject: [PATCH] Fix user struct leakage with locked IPC shem segment
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@...nvz.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@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists