Re: [syzbot] [mm?] KASAN: slab-use-after-free Read in finish_fault

From: Baolin Wang
Date: Thu Jun 13 2024 - 08:12:38 EST




On 2024/6/13 19:38, syzbot wrote:
Hello,

syzbot found the following issue on:

HEAD commit: d35b2284e966 Add linux-next specific files for 20240607
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=178b77ba980000
kernel config: https://syzkaller.appspot.com/x/.config?x=d8bf5cd6bcca7343
dashboard link: https://syzkaller.appspot.com/bug?extid=d6e5c328862b5ae6cbfe
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=174c680a980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=111b9696980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e0055a00a2cb/disk-d35b2284.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/192cbb8cf833/vmlinux-d35b2284.xz
kernel image: https://storage.googleapis.com/syzbot-assets/57804c9c9319/bzImage-d35b2284.xz

The issue was bisected to:

commit 1c05047ad01693ad92bdf8347fad3b5c2b25e8bb
Author: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Date: Tue Jun 4 10:17:45 2024 +0000

mm: memory: extend finish_fault() to support large folio

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11267f94980000
final oops: https://syzkaller.appspot.com/x/report.txt?x=13267f94980000
console output: https://syzkaller.appspot.com/x/log.txt?x=15267f94980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d6e5c328862b5ae6cbfe@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 1c05047ad016 ("mm: memory: extend finish_fault() to support large folio")

==================================================================
BUG: KASAN: use-after-free in ptep_get include/linux/pgtable.h:317 [inline]
BUG: KASAN: use-after-free in ptep_get_lockless include/linux/pgtable.h:581 [inline]
BUG: KASAN: use-after-free in pte_range_none mm/memory.c:4409 [inline]
BUG: KASAN: use-after-free in finish_fault+0xf87/0x1460 mm/memory.c:4905
Read of size 8 at addr ffff88807bfb7000 by task syz-executor149/5117

CPU: 0 PID: 5117 Comm: syz-executor149 Not tainted 6.10.0-rc2-next-20240607-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:91 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:117
print_address_description mm/kasan/report.c:377 [inline]
print_report+0x169/0x550 mm/kasan/report.c:488
kasan_report+0x143/0x180 mm/kasan/report.c:601
ptep_get include/linux/pgtable.h:317 [inline]
ptep_get_lockless include/linux/pgtable.h:581 [inline]
pte_range_none mm/memory.c:4409 [inline]
finish_fault+0xf87/0x1460 mm/memory.c:4905
do_read_fault mm/memory.c:5052 [inline]
do_fault mm/memory.c:5178 [inline]
do_pte_missing mm/memory.c:3948 [inline]
handle_pte_fault+0x3db5/0x7130 mm/memory.c:5502
__handle_mm_fault mm/memory.c:5645 [inline]
handle_mm_fault+0x10df/0x1ba0 mm/memory.c:5810
faultin_page mm/gup.c:1339 [inline]
__get_user_pages+0x6ef/0x1590 mm/gup.c:1638
populate_vma_page_range+0x264/0x330 mm/gup.c:2078
__mm_populate+0x27a/0x460 mm/gup.c:2181
mm_populate include/linux/mm.h:3442 [inline]
__do_sys_remap_file_pages mm/mmap.c:3177 [inline]
__se_sys_remap_file_pages+0x7a1/0x9a0 mm/mmap.c:3103
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Thanks for reporting. I think the problem is I should also consider the pagetable of PMD size in case the pte entry overflows. I will fix this issue ASAP.