Hmm, I haven't received the original patch. On Wed 16-08-17 21:18:58, zhong jiang wrote: > + stable@xxxxxxxxxxxxxxx Anyway the proper way to route this to the stable tree is to put Cc: stable to the sign-off-by area. It is also preferable if you could add Fixes: sha1 which has caused the issue so that people know to which kernel versions this should be backported. > On 2017/8/16 10:13, zhong jiang wrote: > > I hit an use after free issue by executing trinity. and repoduce it > > with KASAN enabled. The related call trace is as follows. > > > > BUG: KASan: use after free in SyS_get_mempolicy+0x3c8/0x960 at addr ffff8801f582d766 > > Read of size 2 by task syz-executor1/798 > > > > INFO: Allocated in mpol_new.part.2+0x74/0x160 age=3 cpu=1 pid=799 > > __slab_alloc+0x768/0x970 > > kmem_cache_alloc+0x2e7/0x450 > > mpol_new.part.2+0x74/0x160 > > mpol_new+0x66/0x80 > > SyS_mbind+0x267/0x9f0 > > system_call_fastpath+0x16/0x1b > > INFO: Freed in __mpol_put+0x2b/0x40 age=4 cpu=1 pid=799 > > __slab_free+0x495/0x8e0 > > kmem_cache_free+0x2f3/0x4c0 > > __mpol_put+0x2b/0x40 > > SyS_mbind+0x383/0x9f0 > > system_call_fastpath+0x16/0x1b > > INFO: Slab 0xffffea0009cb8dc0 objects=23 used=8 fp=0xffff8801f582de40 flags=0x200000000004080 > > INFO: Object 0xffff8801f582d760 @offset=5984 fp=0xffff8801f582d600 > > > > Bytes b4 ffff8801f582d750: ae 01 ff ff 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ > > Object ffff8801f582d760: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk > > Object ffff8801f582d770: 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkk. > > Redzone ffff8801f582d778: bb bb bb bb bb bb bb bb ........ > > Padding ffff8801f582d8b8: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ > > Memory state around the buggy address: > > ffff8801f582d600: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc > > ffff8801f582d680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > >> ffff8801f582d700: fc fc fc fc fc fc fc fc fc fc fc fc fb fb fb fc > > > > when calling get_mempolicy from userspace, it only hold the mmap_sem > > and increase the shared pol count, the unshared pol is not be increased. > > it premature release the mmap_sem, it will result in the related mempolicy > > maybe had freed by mbind. then, the issue will trigger. This is really hard to read. I assume you meant to say that !shared memory policy is not protected against parallel removal by other thread which is normally protected by the mmap_sem. do_get_mempolicy, however, drops the lock midway while we can still access it later. Early premature up_read is a historical artifact from times when put_user was called in this path see https://lwn.net/Articles/124754/ but that is gone since 8bccd85ffbaf ("[PATCH] Implement sys_* do_* layering in the memory policy layer."). I didn't check since when we have the current mempolicy ref count model though but it is really old... > > The patch fix the issue by removing the premature release. it will safe > > access the mempolicy. The issue will leave. > > > > Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx> The fix looks good to me, feel free to use above information for a better changelog Acked-by: Michal Hocko <mhocko@xxxxxxxx> > > --- > > mm/mempolicy.c | 5 ----- > > 1 file changed, 5 deletions(-) > > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > index d911fa5..618ab12 100644 > > --- a/mm/mempolicy.c > > +++ b/mm/mempolicy.c > > @@ -861,11 +861,6 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, > > *policy |= (pol->flags & MPOL_MODE_FLAGS); > > } > > > > - if (vma) { > > - up_read(¤t->mm->mmap_sem); > > - vma = NULL; > > - } > > - > > err = 0; > > if (nmask) { > > if (mpol_store_user_nodemask(pol)) { > -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
