On 12/31/18 8:51 AM, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: 79fc24ff6184 kmsan: highmem: use kmsan_clear_page() in cop.. > git tree: kmsan > console output: https://syzkaller.appspot.com/x/log.txt?x=13c48b67400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=901dd030b2cc57e7 > dashboard link: https://syzkaller.appspot.com/bug?extid=b19c2dc2c990ea657a71 > compiler: clang version 8.0.0 (trunk 349734) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+b19c2dc2c990ea657a71@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KMSAN: uninit-value in mpol_rebind_policy mm/mempolicy.c:353 [inline] > BUG: KMSAN: uninit-value in mpol_rebind_mm+0x249/0x370 mm/mempolicy.c:384 The report doesn't seem to indicate where the uninit value resides in the mempolicy object. I'll have to guess. mm/mempolicy.c:353 contains: if (!mpol_store_user_nodemask(pol) && nodes_equal(pol->w.cpuset_mems_allowed, *newmask)) "mpol_store_user_nodemask(pol)" is testing pol->flags, which I couldn't see being uninitialized after leaving mpol_new(). So I'll guess it's actually about accessing pol->w.cpuset_mems_allowed on line 354. For w.cpuset_mems_allowed to be not initialized and the nodes_equal() reachable for a mempolicy where mpol_set_nodemask() is called in do_mbind(), it seems the only possibility is a MPOL_PREFERRED policy with empty set of nodes, i.e. MPOL_LOCAL equivalent. Let's see if the patch below helps. This code is a maze to me. Note the uninit access should be benign, rebinding this kind of policy is always a no-op. ----8<---- >From ff0ca29da6bc2572d7b267daa77ced6083e3f02d Mon Sep 17 00:00:00 2001 From: Vlastimil Babka <vbabka@xxxxxxx> Date: Thu, 3 Jan 2019 09:31:59 +0100 Subject: [PATCH] mm, mempolicy: fix uninit memory access --- mm/mempolicy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index d4496d9d34f5..a0b7487b9112 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -350,7 +350,7 @@ static void mpol_rebind_policy(struct mempolicy *pol, const nodemask_t *newmask) { if (!pol) return; - if (!mpol_store_user_nodemask(pol) && + if (!mpol_store_user_nodemask(pol) && !(pol->flags & MPOL_F_LOCAL) && nodes_equal(pol->w.cpuset_mems_allowed, *newmask)) return; -- 2.19.2
