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>
diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 4429d25..5e5b296 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -195,6 +195,7 @@
}
extern int mpol_misplaced(struct page *, struct vm_area_struct *, unsigned long);
+extern void mpol_put_task_policy(struct task_struct *);
#else
@@ -297,5 +298,8 @@
return -1; /* no node preference */
}
+static inline void mpol_put_task_policy(struct task_struct *task)
+{
+}
#endif /* CONFIG_NUMA */
#endif
diff --git a/kernel/exit.c b/kernel/exit.c
index 2f974ae..091a78b 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -848,12 +848,7 @@
TASKS_RCU(preempt_enable());
exit_notify(tsk, group_dead);
proc_exit_connector(tsk);
-#ifdef CONFIG_NUMA
- task_lock(tsk);
- mpol_put(tsk->mempolicy);
- tsk->mempolicy = NULL;
- task_unlock(tsk);
-#endif
+ mpol_put_task_policy(tsk);
#ifdef CONFIG_FUTEX
if (unlikely(current->pi_state_cache))
kfree(current->pi_state_cache);
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d8c4e38..2da72a5 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2336,6 +2336,23 @@
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);