Re: [syzbot] general protection fault in shm_close

From: Mike Kravetz
Date: Sun Nov 13 2022 - 23:06:51 EST

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@xxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> 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@xxxxxxxxxxxxxxxx.
>
> 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