path: root/mm
diff options
authorDavid Rientjes <rientjes@google.com>2016-09-01 16:15:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-09-01 17:52:01 -0700
commitc11600e4fed67ae4cd6a8096936afd445410e8ed (patch)
tree0f71f8ca5028621c2615eb83699535fa8b0ffe84 /mm
parent19feeff18bbfde659baa58c2346f15a24d7c405e (diff)
mm, mempolicy: task->mempolicy must be NULL before dropping final reference
KASAN allocates memory from the page allocator as part of kmem_cache_free(), and that can reference current->mempolicy through any number of allocation functions. It needs to be NULL'd out before the final reference is dropped to prevent a use-after-free bug: BUG: KASAN: use-after-free in alloc_pages_current+0x363/0x370 at addr ffff88010b48102c CPU: 0 PID: 15425 Comm: trinity-c2 Not tainted 4.8.0-rc2+ #140 ... Call Trace: dump_stack kasan_object_err kasan_report_error __asan_report_load2_noabort alloc_pages_current <-- use after free depot_save_stack save_stack kasan_slab_free kmem_cache_free __mpol_put <-- free do_exit This patch sets current->mempolicy to NULL before dropping the final reference. Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1608301442180.63329@chino.kir.corp.google.com Fixes: cd11016e5f52 ("mm, kasan: stackdepot implementation. Enable stackdepot for SLAB") Signed-off-by: David Rientjes <rientjes@google.com> Reported-by: Vegard Nossum <vegard.nossum@oracle.com> Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Alexander Potapenko <glider@google.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: <stable@vger.kernel.org> [4.6+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 17 insertions, 0 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d8c4e38fb5f4..2da72a5b6ecc 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2336,6 +2336,23 @@ out:
return ret;
+ * Drop the (possibly final) reference to task->mempolicy. It needs to be
+ * dropped after task->mempolicy is set to NULL so that any allocation done as
+ * part of its kmem_cache_free(), such as by KASAN, doesn't reference a freed
+ * policy.
+ */
+void mpol_put_task_policy(struct task_struct *task)
+ struct mempolicy *pol;
+ task_lock(task);
+ pol = task->mempolicy;
+ task->mempolicy = NULL;
+ task_unlock(task);
+ mpol_put(pol);
static void sp_delete(struct shared_policy *sp, struct sp_node *n)
pr_debug("deleting %lx-l%lx\n", n->start, n->end);