Re: [syzbot] general protection fault in vma_is_shmem

[Andrew Morton]

On Sat, 20 Aug 2022 23:14:24 -0700 syzbot <syzbot+681bbbb80445ead3c040@xxxxxxxxxxxxxxxxxxxxxxxxx> 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+681bbbb80445ead3c040@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> 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.


> 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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> 
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