From: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Subject: stackdepot: fix mempolicy use-after-free
This patch fixes the following:
BUG: KASAN: use-after-free in alloc_pages_current+0x363/0x370 at addr ffff88010b48102c
Read of size 2 by task trinity-c2/15425
CPU: 0 PID: 15425 Comm: trinity-c2 Not tainted 4.8.0-rc2+ #140
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-proje
ct.org 04/01/2014
ffff88010b481040 ffff88010b557650 ffffffff81f08d11 ffff88011a40d380
ffff88010b481028 ffff88010b557678 ffffffff815dac7c ffff88010b557708
ffff88010b481028 ffff88011a40d380 ffff88010b5576f8 ffffffff815daf15
Call Trace:
[<ffffffff81f08d11>] dump_stack+0x65/0x84
[<ffffffff815dac7c>] kasan_object_err+0x1c/0x70
[<ffffffff815daf15>] kasan_report_error+0x1f5/0x4c0
[<ffffffff815db2fe>] __asan_report_load2_noabort+0x3e/0x40
[<ffffffff815cb903>] alloc_pages_current+0x363/0x370 <---- use-after-free
[<ffffffff81fa9954>] depot_save_stack+0x3f4/0x490
[<ffffffff815d9bb5>] save_stack+0xb5/0xd0
[<ffffffff815da211>] kasan_slab_free+0x71/0xb0
[<ffffffff815d6643>] kmem_cache_free+0xa3/0x290
[<ffffffff815c8149>] __mpol_put+0x19/0x20 <---- free
[<ffffffff81260635>] do_exit+0x1515/0x2b70
[<ffffffff81261dc4>] do_group_exit+0xf4/0x2f0
[<ffffffff81281c5d>] get_signal+0x53d/0x1120
[<ffffffff8119e993>] do_signal+0x83/0x1e20
[<ffffffff810027af>] exit_to_usermode_loop+0xaf/0x140
[<ffffffff810051e4>] syscall_return_slowpath+0x144/0x170
[<ffffffff83ae406f>] ret_from_fork+0x2f/0x40
Read of size 2 by task trinity-c2/15425
The problem is that we may be calling alloc_pages() in a code path where
current->mempolicy has already been freed.
By passing __GFP_THISNODE we will always use default_mempolicy (which
cannot be freed).
Link: https://lkml.org/lkml/2016/7/29/277
Link: https://github.com/google/kasan/issues/35
Link: http://lkml.kernel.org/r/1471603265-31804-1-git-send-email-vegard.nossum@xxxxxxxxxx
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Acked-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/stackdepot.c | 6 ++++++
1 file changed, 6 insertions(+)
diff -puN lib/stackdepot.c~stackdepot-fix-mempolicy-use-after-free lib/stackdepot.c
--- a/lib/stackdepot.c~stackdepot-fix-mempolicy-use-after-free
+++ a/lib/stackdepot.c
@@ -243,6 +243,12 @@ depot_stack_handle_t depot_save_stack(st
alloc_flags &= ~GFP_ZONEMASK;
alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
alloc_flags |= __GFP_NOWARN;
+ /*
+ * Avoid using current->mempolicy which may already have
+ * been freed -- we may be in the process of saving the
+ * stack for exactly that __mpol_put() call.
+ */
+ alloc_flags |= __GFP_THISNODE;
page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
if (page)
prealloc = page_address(page);
_
--
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