Re: [syzbot] [nilfs?] general protection fault in __d_unalias

[Ryusuke Konishi]

On Tue, Feb 4, 2025 at 3:55 AM syzbot
<syzbot+ab57f676a518849a8d57@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    69b8923f5003 Merge tag 'for-linus-6.14-ofs4' of git://git...
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14fbdddf980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=57ab43c279fa614d
> dashboard link: https://syzkaller.appspot.com/bug?extid=ab57f676a518849a8d57
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15da95f8580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=165f8b24580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/ea84ac864e92/disk-69b8923f.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/6a465997b4e0/vmlinux-69b8923f.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d72b67b2bd15/bzImage-69b8923f.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/7d96d510aa23/mount_0.gz
>
> The issue was bisected to:
>
> commit 30d61efe118cad1a73ad2ad66a3298e4abdf9f41
> Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Date:   Mon Jan 6 02:33:17 2025 +0000
>
>     9p: fix ->rename_sem exclusion
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=148b7b64580000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=168b7b64580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=128b7b64580000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ab57f676a518849a8d57@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 30d61efe118c ("9p: fix ->rename_sem exclusion")
>
> Oops: general protection fault, probably for non-canonical address 0xdffffc000000000d: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f]
> CPU: 0 UID: 0 PID: 5821 Comm: syz-executor287 Not tainted 6.13.0-syzkaller-09793-g69b8923f5003 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
> RIP: 0010:__d_unalias+0x199/0x2a0 fs/dcache.c:2969
> Code: 98 00 00 00 4c 89 fb 48 c1 eb 03 49 89 ed 80 3c 2b 00 74 08 4c 89 ff e8 65 62 e7 ff 49 8b 2f 48 83 c5 68 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 48 62 e7 ff 4c 8b 5d 00 4d 85 db
> RSP: 0018:ffffc90003d9fa98 EFLAGS: 00010202
> RAX: 000000000000000d RBX: 1ffff1100996cb61 RCX: ffff88804d821e00
> RDX: 0000000000000000 RSI: ffff88804cb65a70 RDI: ffff88804cb658f8
> RBP: 0000000000000068 R08: ffff88804e530f6b R09: 1ffff11009ca61ed
> R10: dffffc0000000000 R11: ffffed1009ca61ee R12: ffff88804cb65a70
> R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88804cb65b08
> FS:  000055555b892380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffe074ff000 CR3: 0000000078440000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  d_splice_alias+0x1e6/0x330 fs/dcache.c:3037
>  nilfs_lookup+0x1c2/0x2a0 fs/nilfs2/namei.c:77
>  lookup_one_qstr_excl+0x126/0x2b0 fs/namei.c:1693
>  do_renameat2+0x706/0x13f0 fs/namei.c:5176
>  __do_sys_rename fs/namei.c:5273 [inline]
>  __se_sys_rename fs/namei.c:5271 [inline]
>  __x64_sys_rename+0x82/0x90 fs/namei.c:5271
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f7cc482fad9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 17 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffe074fe328 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
> RAX: ffffffffffffffda RBX: 00007f7cc4878fc8 RCX: 00007f7cc482fad9
> RDX: 0000000000000000 RSI: 0000000020000800 RDI: 00000000200001c0
> RBP: 00007f7cc48a35f0 R08: 000055555b8934c0 R09: 000055555b8934c0
> R10: 000055555b8934c0 R11: 0000000000000246 R12: 00007ffe074fe350
> R13: 00007ffe074fe578 R14: 431bde82d7b634db R15: 00007f7cc487803b
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:__d_unalias+0x199/0x2a0 fs/dcache.c:2969
> Code: 98 00 00 00 4c 89 fb 48 c1 eb 03 49 89 ed 80 3c 2b 00 74 08 4c 89 ff e8 65 62 e7 ff 49 8b 2f 48 83 c5 68 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 48 62 e7 ff 4c 8b 5d 00 4d 85 db
> RSP: 0018:ffffc90003d9fa98 EFLAGS: 00010202
> RAX: 000000000000000d RBX: 1ffff1100996cb61 RCX: ffff88804d821e00
> RDX: 0000000000000000 RSI: ffff88804cb65a70 RDI: ffff88804cb658f8
> RBP: 0000000000000068 R08: ffff88804e530f6b R09: 1ffff11009ca61ed
> R10: dffffc0000000000 R11: ffffed1009ca61ee R12: ffff88804cb65a70
> R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88804cb65b08
> FS:  000055555b892380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffe074ff000 CR3: 0000000078440000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:   98                      cwtl
>    1:   00 00                   add    %al,(%rax)
>    3:   00 4c 89 fb             add    %cl,-0x5(%rcx,%rcx,4)
>    7:   48 c1 eb 03             shr    $0x3,%rbx
>    b:   49 89 ed                mov    %rbp,%r13
>    e:   80 3c 2b 00             cmpb   $0x0,(%rbx,%rbp,1)
>   12:   74 08                   je     0x1c
>   14:   4c 89 ff                mov    %r15,%rdi
>   17:   e8 65 62 e7 ff          call   0xffe76281
>   1c:   49 8b 2f                mov    (%r15),%rbp
>   1f:   48 83 c5 68             add    $0x68,%rbp
>   23:   48 89 e8                mov    %rbp,%rax
>   26:   48 c1 e8 03             shr    $0x3,%rax
> * 2a:   42 80 3c 28 00          cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
>   2f:   74 08                   je     0x39
>   31:   48 89 ef                mov    %rbp,%rdi
>   34:   e8 48 62 e7 ff          call   0xffe76281
>   39:   4c 8b 5d 00             mov    0x0(%rbp),%r11
>   3d:   4d 85 db                test   %r11,%r11
>
>
> ---
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>
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>
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I tested reproducers locally and found that the issue was fixed with
the latest commit:

#syz fix: fix braino in "9p: fix ->rename_sem exclusion"

Ryusuke Konishi