On Thu 17-08-17 14:22:04, 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 > > !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."). but when we have the the current mempolicy ref > count model. The issue was introduced accordingly. > > The patch fix the issue by removing the premature release. it will safe > access the mempolicy. The issue will leave. > > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Vlastimil Babka <vbabka@xxxxxxx> > Cc: David Rientjes <rientjes@xxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> [2.6+] Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > v1->v2 > - changelog is modified as Michal suggestion. > > 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)) { > -- > 1.7.12.4 -- 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>
