[syzbot] general protection fault in vma_is_shmem

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 95d10484d66e Add linux-next specific files for 20220817
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15133023080000
kernel config: https://syzkaller.appspot.com/x/.config?x=2f5fa747986be53a
dashboard link: https://syzkaller.appspot.com/bug?extid=681bbbb80445ead3c040
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1100a92d080000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=123d1867080000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+681bbb...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
CPU: 1 PID: 3607 Comm: syz-executor359 Not tainted 6.0.0-rc1-next-20220817-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
RIP: 0010:vma_is_shmem+0x21/0x40 mm/shmem.c:254
Code: 73 02 e9 20 fc ff ff 66 90 53 48 89 fb e8 07 2c cf ff 48 8d bb 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 10 48 81 bb 90 00 00 00 20 8f f7 89 5b 0f 94 c0 c3
RSP: 0018:ffffc900037cfb68 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000012 RSI: ffffffff81ace949 RDI: 0000000000000090
RBP: ffff888071b00720 R08: 0000000000000006 R09: 00000000000000e4
R10: 0000000000008001 R11: 0000000000000000 R12: 00000000000000e4
R13: ffff888071b00000 R14: dffffc0000000000 R15: 0000000000000000
FS: 0000555556ab5300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa3c8f13260 CR3: 00000000718f5000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
io_pin_pages+0x25f/0x430 io_uring/rsrc.c:1207
io_sqe_buffer_register+0x14e/0x13b0 io_uring/rsrc.c:1254
io_sqe_buffers_register.cold+0x351/0x445 io_uring/rsrc.c:1346
__io_uring_register io_uring/io_uring.c:3711 [inline]
__do_sys_io_uring_register+0x96d/0x1110 io_uring/io_uring.c:3878
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f548fcdfbb9
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc644b88f8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f548fcdfbb9
RDX: 0000000020000080 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f548fca3d60 R08: 0000000010000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 00007f548fca3df0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:vma_is_shmem+0x21/0x40 mm/shmem.c:254
Code: 73 02 e9 20 fc ff ff 66 90 53 48 89 fb e8 07 2c cf ff 48 8d bb 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 10 48 81 bb 90 00 00 00 20 8f f7 89 5b 0f 94 c0 c3
RSP: 0018:ffffc900037cfb68 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000012 RSI: ffffffff81ace949 RDI: 0000000000000090
RBP: ffff888071b00720 R08: 0000000000000006 R09: 00000000000000e4
R10: 0000000000008001 R11: 0000000000000000 R12: 00000000000000e4
R13: ffff888071b00000 R14: dffffc0000000000 R15: 0000000000000000
FS: 0000555556ab5300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa3c8f13260 CR3: 00000000718f5000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 73 02 jae 0x4
2: e9 20 fc ff ff jmpq 0xfffffc27
7: 66 90 xchg %ax,%ax
9: 53 push %rbx
a: 48 89 fb mov %rdi,%rbx
d: e8 07 2c cf ff callq 0xffcf2c19
12: 48 8d bb 90 00 00 00 lea 0x90(%rbx),%rdi
19: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
20: fc ff df
23: 48 89 fa mov %rdi,%rdx
26: 48 c1 ea 03 shr $0x3,%rdx
* 2a: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction
2e: 75 10 jne 0x40
30: 48 81 bb 90 00 00 00 cmpq $0xffffffff89f78f20,0x90(%rbx)
37: 20 8f f7 89
3b: 5b pop %rbx
3c: 0f 94 c0 sete %al
3f: c3 retq


---
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[Andrew Morton]

On Sat, 20 Aug 2022 23:14:24 -0700 syzbot <syzbot+681bbb...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following issue on:

Thanks. Will a bisection search be performed?

> HEAD commit: 95d10484d66e Add linux-next specific files for 20220817
> git tree: linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=15133023080000
> kernel config: https://syzkaller.appspot.com/x/.config?x=2f5fa747986be53a
> dashboard link: https://syzkaller.appspot.com/bug?extid=681bbbb80445ead3c040
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1100a92d080000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=123d1867080000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+681bbb...@syzkaller.appspotmail.com
>
> general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]

Seems that io_pin_pages->pin_user_pages gave us a null vma* in the
vmas[] array. We haven't messed with gup.c much this time around -
just one patch from Alistair ("mm/gup.c: simplify and fix
check_and_migrate_movable_pages() return codes"). It does touch this
area, but I can't immediately see how it could newly cause this.

[John Hubbard]

On 8/21/22 01:32, Andrew Morton wrote:
> On Sat, 20 Aug 2022 23:14:24 -0700 syzbot <syzbot+681bbb...@syzkaller.appspotmail.com> wrote:
>
>> Hello,
>>
>> syzbot found the following issue on:
>
> Thanks. Will a bisection search be performed?
>
>> HEAD commit: 95d10484d66e Add linux-next specific files for 20220817
>> git tree: linux-next
>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=15133023080000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=2f5fa747986be53a
>> dashboard link: https://syzkaller.appspot.com/bug?extid=681bbbb80445ead3c040
>> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1100a92d080000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=123d1867080000
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+681bbb...@syzkaller.appspotmail.com
>>
>> general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN
>> KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
>
> Seems that io_pin_pages->pin_user_pages gave us a null vma* in the

Agreed.

> vmas[] array. We haven't messed with gup.c much this time around -
> just one patch from Alistair ("mm/gup.c: simplify and fix
> check_and_migrate_movable_pages() return codes"). It does touch this
> area, but I can't immediately see how it could newly cause this.
>

Neither can I, even after looking at both of these recent commits to
gup.c in this branch:

commit 4d1225cd5560 ("mm/gup.c: simplify and fix
check_and_migrate_movable_pages() return codes")

commit 0e5d6dac6b65 ("mm/gup: fix FOLL_FORCE COW security issue and
remove FOLL_COW")

As you say, a bisection would really help here.

thanks,
--
John Hubbard
NVIDIA

[Andrew Morton]

On Sun, 21 Aug 2022 16:18:48 -0700 John Hubbard <jhub...@nvidia.com> wrote:

> > vmas[] array. We haven't messed with gup.c much this time around -
> > just one patch from Alistair ("mm/gup.c: simplify and fix
> > check_and_migrate_movable_pages() return codes"). It does touch this
> > area, but I can't immediately see how it could newly cause this.
> >
>
> Neither can I, even after looking at both of these recent commits to
> gup.c in this branch:
>
> commit 4d1225cd5560 ("mm/gup.c: simplify and fix
> check_and_migrate_movable_pages() return codes")
>
> commit 0e5d6dac6b65 ("mm/gup: fix FOLL_FORCE COW security issue and
> remove FOLL_COW")
>
> As you say, a bisection would really help here.

Might
https://lkml.kernel.org/r/20220821183547.9...@redhat.com
save us?

[John Hubbard]

aha yes, that looks right.

[Aleksandr Nogikh]

Let's tell syzbot about the fix

#syz fix: mm/gup.c: Fix return value for __gup_longterm_locked()

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