Re: [syzbot] general protection fault in shm_close

[Mike Kravetz <mike.kravetz@oracle.com>]

On 11/13/22 19:11, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f8f60f322f06 Add linux-next specific files for 20221111
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=15599bd5880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=85ba52c07cd97289
> dashboard link: https://syzkaller.appspot.com/bug?extid=83b4134621b7c326d950
> 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=15a05e71880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11de4db9880000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/6008df424195/disk-f8f60f32.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/394340525f66/vmlinux-f8f60f32.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/b13604a3343a/bzImage-f8f60f32.xz
> 
> The issue was bisected to:
> 
> commit 6a892ddb84e542931554f4ee9a528190003b23a0
> Author: Mike Kravetz <mike.kravetz@oracle.com>
> Date:   Thu Nov 10 00:21:50 2022 +0000
> 
>     ipc/shm: call underlying open/close vm_ops
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14a0f199880000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=16a0f199880000
> console output: https://syzkaller.appspot.com/x/log.txt?x=12a0f199880000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+83b4134621b7c326d950@syzkaller.appspotmail.com
> Fixes: 6a892ddb84e5 ("ipc/shm: call underlying open/close vm_ops")
> 
> general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> CPU: 0 PID: 5247 Comm: syz-executor310 Not tainted 6.1.0-rc4-next-20221111-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> RIP: 0010:shm_close+0xbf/0x740 ipc/shm.c:378
> Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 1c 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 5d 18 48 8d 7b 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 db 05 00 00 48 8b 5b 08 48 85 db 74 0a e8 99 7c
> RSP: 0018:ffffc90003e0fba0 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000001 RSI: ffffffff83bf5016 RDI: 0000000000000008
> RBP: ffff8880296a2d40 R08: 0000000000000005 R09: 0000000000000000
> R10: 00000000fffffff4 R11: 0000000000000000 R12: ffff8880263fb1c0
> R13: ffffffff8c7a97a0 R14: 0000000000000008 R15: ffffc90003e0fca0
> FS:  0000555555992300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fde9cc15348 CR3: 0000000025865000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  shm_mmap+0x1c2/0x230 ipc/shm.c:604

shm_mmap has this code block:

	ret = __shm_open(vma);
	if (ret)
		return ret;

	ret = call_mmap(sfd->file, vma);
	if (ret) {
		shm_close(vma);
		return ret;
	}
	sfd->vm_ops = vma->vm_ops;

In the case of call_mmap error, it calls shm_close BEFORE setting up
sfd->vm_ops.  So, shm_close is going to have problems when doing:

	if (sfd->vm_ops->close)
		sfd->vm_ops->close(vma);

I will put together a fix tomorrow and take a closer look at all the
error paths.
-- 
Mike Kravetz

>  call_mmap include/linux/fs.h:2164 [inline]
>  mmap_region+0x6bf/0x1dc0 mm/mmap.c:2625
>  do_mmap+0x825/0xf50 mm/mmap.c:1412
>  do_shmat+0xe33/0x10c0 ipc/shm.c:1661
>  __do_sys_shmat ipc/shm.c:1697 [inline]
>  __se_sys_shmat ipc/shm.c:1692 [inline]
>  __x64_sys_shmat+0xcc/0x160 ipc/shm.c:1692
>  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: 0033:0x7fde9cba2cf9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 90 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:00007fff3ed491f8 EFLAGS: 00000246 ORIG_RAX: 000000000000001e
> RAX: ffffffffffffffda RBX: 000000000000cfd6 RCX: 00007fde9cba2cf9
> RDX: ffffffffffffcfff RSI: 0000000020000000 RDI: 0000000000000008
> RBP: 0000000000000000 R08: 00007fff3ed49398 R09: 00007fff3ed49398
> R10: 00007fff3ed48c70 R11: 0000000000000246 R12: 00007fff3ed4920c
> R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:shm_close+0xbf/0x740 ipc/shm.c:378
> Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 1c 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 5d 18 48 8d 7b 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 db 05 00 00 48 8b 5b 08 48 85 db 74 0a e8 99 7c
> RSP: 0018:ffffc90003e0fba0 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000001 RSI: ffffffff83bf5016 RDI: 0000000000000008
> RBP: ffff8880296a2d40 R08: 0000000000000005 R09: 0000000000000000
> R10: 00000000fffffff4 R11: 0000000000000000 R12: ffff8880263fb1c0
> R13: ffffffff8c7a97a0 R14: 0000000000000008 R15: ffffc90003e0fca0
> FS:  0000555555992300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fff3ed491d8 CR3: 0000000025865000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:	48 89 fa             	mov    %rdi,%rdx
>    3:	48 c1 ea 03          	shr    $0x3,%rdx
>    7:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
>    b:	0f 85 1c 06 00 00    	jne    0x62d
>   11:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
>   18:	fc ff df
>   1b:	48 8b 5d 18          	mov    0x18(%rbp),%rbx
>   1f:	48 8d 7b 08          	lea    0x8(%rbx),%rdi
>   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:	0f 85 db 05 00 00    	jne    0x60f
>   34:	48 8b 5b 08          	mov    0x8(%rbx),%rbx
>   38:	48 85 db             	test   %rbx,%rbx
>   3b:	74 0a                	je     0x47
>   3d:	e8                   	.byte 0xe8
>   3e:	99                   	cltd
>   3f:	7c                   	.byte 0x7c
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches