KASAN: null-ptr-deref Read in PageHuge

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6b02addb Add linux-next specific files for 20200915
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17a7441d900000
kernel config: https://syzkaller.appspot.com/x/.config?x=7086d0e9e44d4a14
dashboard link: https://syzkaller.appspot.com/bug?extid=3a21fd5ecfc677248e77
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=141489f1900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1694fd55900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3a21fd...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:71 [inline]
BUG: KASAN: null-ptr-deref in test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline]
BUG: KASAN: null-ptr-deref in PageCompound include/linux/page-flags.h:196 [inline]
BUG: KASAN: null-ptr-deref in PageHuge+0x19/0x170 mm/hugetlb.c:1551
Read of size 8 at addr 0000000000000000 by task syz-executor410/6864

CPU: 1 PID: 6864 Comm: syz-executor410 Not tainted 5.9.0-rc5-next-20200915-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x198/0x1fb lib/dump_stack.c:118
__kasan_report mm/kasan/report.c:549 [inline]
kasan_report.cold+0x5/0x37 mm/kasan/report.c:562
check_memory_region_inline mm/kasan/generic.c:186 [inline]
check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
instrument_atomic_read include/linux/instrumented.h:71 [inline]
test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline]
PageCompound include/linux/page-flags.h:196 [inline]
PageHuge+0x19/0x170 mm/hugetlb.c:1551
find_subpage include/linux/pagemap.h:410 [inline]
find_get_incore_page+0x165/0x2e0 mm/swap_state.c:435
mincore_page+0x1e/0x310 mm/mincore.c:62
__mincore_unmapped_range+0x171/0x2c0 mm/mincore.c:82
mincore_pte_range+0x69f/0x980 mm/mincore.c:125
walk_pmd_range mm/pagewalk.c:89 [inline]
walk_pud_range mm/pagewalk.c:160 [inline]
walk_p4d_range mm/pagewalk.c:193 [inline]
walk_pgd_range mm/pagewalk.c:229 [inline]
__walk_page_range+0xeed/0x22c0 mm/pagewalk.c:331
walk_page_range+0x20d/0x400 mm/pagewalk.c:427
do_mincore mm/mincore.c:199 [inline]
__do_sys_mincore+0x279/0x7a0 mm/mincore.c:264
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x440329
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe6fca7ae8 EFLAGS: 00000246 ORIG_RAX: 000000000000001b
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440329
RDX: 0000000000000000 RSI: 0000000000004000 RDI: 0000000020001000
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000401b30
R13: 0000000000401bc0 R14: 0000000000000000 R15: 0000000000000000
==================================================================


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[Mike Kravetz]

I assume this would also be fixed by 5d1903f712ac
("mm-convert-find_get_entry-to-return-the-head-page-fix")

--
Mike Kravetz

[Matthew Wilcox]

On Fri, Sep 18, 2020 at 12:42:24PM -0700, Mike Kravetz wrote:
> On 9/18/20 4:02 AM, syzbot wrote:
> > ==================================================================
> > BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:71 [inline]
> > BUG: KASAN: null-ptr-deref in test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline]
> > BUG: KASAN: null-ptr-deref in PageCompound include/linux/page-flags.h:196 [inline]
> > BUG: KASAN: null-ptr-deref in PageHuge+0x19/0x170 mm/hugetlb.c:1551
> > Read of size 8 at addr 0000000000000000 by task syz-executor410/6864
> >
>

> I assume this would also be fixed by 5d1903f712ac
> ("mm-convert-find_get_entry-to-return-the-head-page-fix")

That's a good bet.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+3a21fd...@syzkaller.appspotmail.com

Tested on:

commit: 92ab97ad Merge tag 'sh-for-5.9-part2' of git://git.libc.or..
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=3c1106ec7339554a

dashboard link: https://syzkaller.appspot.com/bug?extid=3a21fd5ecfc677248e77
compiler: gcc (GCC) 10.1.0-syz 20200507

Note: testing is done by a robot and is best-effort only.

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.