This is a note to let you know that I've just added the patch titled mm, mempolicy: task->mempolicy must be NULL before dropping final reference to the 4.7-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-mempolicy-task-mempolicy-must-be-null-before-dropping-final-reference.patch and it can be found in the queue-4.7 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From c11600e4fed67ae4cd6a8096936afd445410e8ed Mon Sep 17 00:00:00 2001 From: David Rientjes <rientjes@xxxxxxxxxx> Date: Thu, 1 Sep 2016 16:15:07 -0700 Subject: mm, mempolicy: task->mempolicy must be NULL before dropping final reference From: David Rientjes <rientjes@xxxxxxxxxx> commit c11600e4fed67ae4cd6a8096936afd445410e8ed upstream. 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@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: cd11016e5f52 ("mm, kasan: stackdepot implementation. Enable stackdepot for SLAB") Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> Reported-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx> Acked-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/mempolicy.h | 4 ++++ kernel/exit.c | 7 +------ mm/mempolicy.c | 17 +++++++++++++++++ 3 files changed, 22 insertions(+), 6 deletions(-) --- a/include/linux/mempolicy.h +++ b/include/linux/mempolicy.h @@ -195,6 +195,7 @@ static inline bool vma_migratable(struct } 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 @@ static inline int mpol_misplaced(struct return -1; /* no node preference */ } +static inline void mpol_put_task_policy(struct task_struct *task) +{ +} #endif /* CONFIG_NUMA */ #endif --- a/kernel/exit.c +++ b/kernel/exit.c @@ -768,12 +768,7 @@ void do_exit(long code) 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); --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2334,6 +2334,23 @@ 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); Patches currently in stable-queue which might be from rientjes@xxxxxxxxxx are queue-4.7/mm-oom-prevent-premature-oom-killer-invocation-for-high-order-request.patch queue-4.7/mm-mempolicy-task-mempolicy-must-be-null-before-dropping-final-reference.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html