Re: [syzbot] general protection fault in nilfs_bmap_lookup_at_level

[Ryusuke Konishi]

On Sat, Oct 1, 2022 at 7:27 AM syzbot wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    aaa11ce2ffc8 Add linux-next specific files for 20220923
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=12904574880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=186d1ff305f10294
> dashboard link: https://syzkaller.appspot.com/bug?extid=76f0ebea6c1e032bbe49
> 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=1181a5c4880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12bdc2e0880000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/95c7bf83c07e/disk-aaa11ce2.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b161cd56a7a3/vmlinux-aaa11ce2.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+76f0ebea6c1e032bbe49@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> loop0: detected capacity change from 0 to 2048
> general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 0 PID: 3609 Comm: syz-executor421 Not tainted 6.0.0-rc6-next-20220923-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022
> RIP: 0010:nilfs_bmap_lookup_at_level+0xb5/0x3e0 fs/nilfs2/bmap.c:69
> Code: df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 95 02 00 00 48 8b 83 d8 00 00 00 48 ba 00 00 00 00 00 fc ff df 48 89 c1 48 c1 e9 03 <80> 3c 11 00 0f 85 7d 02 00 00 4c 89 e6 48 89 e9 44 89 fa 48 89 df
> RSP: 0018:ffffc90003caf6d8 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff8880738da688 RCX: 0000000000000000
> RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff8880738da760
> RBP: ffffc90003caf7b8 R08: 0000000000000001 R09: ffff8880738da6cf
> R10: ffffed100e71b4d9 R11: 000000000008c07e R12: 0000000000000002
> R13: 1ffff92000795edc R14: ffff8880738da6c0 R15: 0000000000000001
> FS:  0000555555ac8300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000005d84c8 CR3: 000000005942f000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  nilfs_bmap_lookup fs/nilfs2/bmap.h:170 [inline]
>  nilfs_mdt_submit_block+0x1a1/0xb40 fs/nilfs2/mdt.c:142
>  nilfs_mdt_read_block+0x92/0x3c0 fs/nilfs2/mdt.c:176
>  nilfs_mdt_get_block+0xe3/0xe00 fs/nilfs2/mdt.c:251
>  nilfs_palloc_get_block+0xc4/0x2b0 fs/nilfs2/alloc.c:216
>  nilfs_palloc_get_entry_block+0x167/0x1d0 fs/nilfs2/alloc.c:318
>  nilfs_ifile_get_inode_block+0xbf/0x190 fs/nilfs2/ifile.c:143
>  __nilfs_read_inode fs/nilfs2/inode.c:477 [inline]
>  nilfs_iget+0x208/0x870 fs/nilfs2/inode.c:603
>  nilfs_get_root_dentry+0x26/0x240 fs/nilfs2/super.c:904
>  nilfs_fill_super fs/nilfs2/super.c:1078 [inline]
>  nilfs_mount+0xbb2/0xfb0 fs/nilfs2/super.c:1317
>  legacy_get_tree+0x105/0x220 fs/fs_context.c:610
>  vfs_get_tree+0x89/0x2f0 fs/super.c:1530
>  do_new_mount fs/namespace.c:3040 [inline]
>  path_mount+0x1326/0x1e20 fs/namespace.c:3370
>  do_mount fs/namespace.c:3383 [inline]
>  __do_sys_mount fs/namespace.c:3591 [inline]
>  __se_sys_mount fs/namespace.c:3568 [inline]
>  __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
>  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: 0033:0x7fd84078b60a
> Code: 83 c4 08 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 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:00007ffc2a043bd8 EFLAGS: 00000286 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fd84078b60a
> RDX: 0000000020000000 RSI: 0000000020000080 RDI: 00007ffc2a043bf0
> RBP: 00007ffc2a043bf0 R08: 00007ffc2a043c30 R09: 0000555555ac82c0
> R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000000004
> R13: 00007ffc2a043c30 R14: 000000000000003a R15: 0000000020000770
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:nilfs_bmap_lookup_at_level+0xb5/0x3e0 fs/nilfs2/bmap.c:69
> Code: df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 95 02 00 00 48 8b 83 d8 00 00 00 48 ba 00 00 00 00 00 fc ff df 48 89 c1 48 c1 e9 03 <80> 3c 11 00 0f 85 7d 02 00 00 4c 89 e6 48 89 e9 44 89 fa 48 89 df
> RSP: 0018:ffffc90003caf6d8 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff8880738da688 RCX: 0000000000000000
> RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff8880738da760
> RBP: ffffc90003caf7b8 R08: 0000000000000001 R09: ffff8880738da6cf
> R10: ffffed100e71b4d9 R11: 000000000008c07e R12: 0000000000000002
> R13: 1ffff92000795edc R14: ffff8880738da6c0 R15: 0000000000000001
> FS:  0000555555ac8300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000005d84c8 CR3: 000000005942f000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:   df 48 89                fisttps -0x77(%rax)
>    3:   fa                      cli
>    4:   48 c1 ea 03             shr    $0x3,%rdx
>    8:   80 3c 02 00             cmpb   $0x0,(%rdx,%rax,1)
>    c:   0f 85 95 02 00 00       jne    0x2a7
>   12:   48 8b 83 d8 00 00 00    mov    0xd8(%rbx),%rax
>   19:   48 ba 00 00 00 00 00    movabs $0xdffffc0000000000,%rdx
>   20:   fc ff df
>   23:   48 89 c1                mov    %rax,%rcx
>   26:   48 c1 e9 03             shr    $0x3,%rcx
> * 2a:   80 3c 11 00             cmpb   $0x0,(%rcx,%rdx,1) <-- trapping instruction
>   2e:   0f 85 7d 02 00 00       jne    0x2b1
>   34:   4c 89 e6                mov    %r12,%rsi
>   37:   48 89 e9                mov    %rbp,%rcx
>   3a:   44 89 fa                mov    %r15d,%edx
>   3d:   48 89 df                mov    %rbx,%rdi
>
>
> ---
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> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
>
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> syzbot can test patches for this issue, for details see:
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#syz dup: INFO: trying to register non-static key in nilfs_bmap_lookup_at_level

I confirmed that the patch titled "nilfs2: fix NULL pointer
dereference at nilfs_bmap_lookup_at_level()" which I submitted for the
above issue also fixes this oops.

Ryusuke Konishi