Re: [syzbot] [overlayfs?] general protection fault in ovl_real_file_path

[Amir Goldstein]

On Mon, Oct 14, 2024 at 10:58 AM syzbot
<syzbot+aaf95b6e8fc9d906d8a7@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    d61a00525464 Add linux-next specific files for 20241011
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1688fb27980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8554528c7f4bf3fb
> dashboard link: https://syzkaller.appspot.com/bug?extid=aaf95b6e8fc9d906d8a7
> 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=10d5705f980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1188fb27980000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f615720e9964/disk-d61a0052.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/c4a45c7583c6/vmlinux-d61a0052.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d767ab86d0d0/bzImage-d61a0052.xz
>
> The issue was bisected to:
>
> commit 181d71062eef699385d92b92f8ad3cbf03e61267
> Author: Amir Goldstein <amir73il@xxxxxxxxx>
> Date:   Mon Oct 7 13:22:29 2024 +0000
>
>     ovl: allocate a container struct ovl_file for ovl private context
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11c41440580000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13c41440580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=15c41440580000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+aaf95b6e8fc9d906d8a7@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 181d71062eef ("ovl: allocate a container struct ovl_file for ovl private context")
>
> 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: 1 UID: 0 PID: 5235 Comm: syz-executor410 Not tainted 6.12.0-rc2-next-20241011-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> RIP: 0010:file_inode include/linux/fs.h:1124 [inline]
> RIP: 0010:ovl_is_real_file fs/overlayfs/file.c:100 [inline]
> RIP: 0010:ovl_real_file_path+0xa5/0x2e0 fs/overlayfs/file.c:118
> Code: 03 4d 89 f7 42 80 3c 30 00 74 08 4c 89 ef e8 22 1e e0 fe 4c 89 64 24 10 49 8b 45 00 49 89 c4 4c 8d 70 68 4c 89 f0 48 c1 e8 03 <42> 80 3c 38 00 74 08 4c 89 f7 e8 fc 1d e0 fe 49 8b 1e 48 83 c5 68
> RSP: 0018:ffffc90002dcfb28 EFLAGS: 00010202
> RAX: 000000000000000d RBX: 1ffff920005b9f79 RCX: ffff88801efa5a00
> RDX: 0000000000000000 RSI: ffffc90002dcfbc0 RDI: ffff888031c9bc00
> RBP: ffff88807eb938f8 R08: ffffffff831d82d9 R09: 0000000000000000
> R10: ffffc90002dcfae0 R11: fffff520005b9f5e R12: 0000000000000000
> R13: ffff888078c80000 R14: 0000000000000068 R15: dffffc0000000000
> FS:  0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020001740 CR3: 000000000e736000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  ovl_real_file+0x186/0x210 fs/overlayfs/file.c:176
>  ovl_flush+0x22/0x140 fs/overlayfs/file.c:620
>  filp_flush+0xb7/0x160 fs/open.c:1527
>  filp_close+0x1e/0x40 fs/open.c:1540
>  close_files fs/file.c:508 [inline]
>  put_files_struct+0x198/0x310 fs/file.c:523
>  do_exit+0xa10/0x28e0 kernel/exit.c:933
>  do_group_exit+0x207/0x2c0 kernel/exit.c:1087
>  __do_sys_exit_group kernel/exit.c:1098 [inline]
>  __se_sys_exit_group kernel/exit.c:1096 [inline]
>  __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1096
>  x64_sys_call+0x2634/0x2640 arch/x86/include/generated/asm/syscalls_64.h:232
>  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: 0033:0x7fbb4c5e7739
> Code: Unable to access opcode bytes at 0x7fbb4c5e770f.
> RSP: 002b:00007fff9c70aac8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fbb4c5e7739
> RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
> RBP: 00007fbb4c662290 R08: ffffffffffffffb8 R09: 00007fbb4c5b5e50
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fbb4c662290
> R13: 0000000000000000 R14: 00007fbb4c662ce0 R15: 00007fbb4c5b62a0
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:file_inode include/linux/fs.h:1124 [inline]
> RIP: 0010:ovl_is_real_file fs/overlayfs/file.c:100 [inline]
> RIP: 0010:ovl_real_file_path+0xa5/0x2e0 fs/overlayfs/file.c:118
> Code: 03 4d 89 f7 42 80 3c 30 00 74 08 4c 89 ef e8 22 1e e0 fe 4c 89 64 24 10 49 8b 45 00 49 89 c4 4c 8d 70 68 4c 89 f0 48 c1 e8 03 <42> 80 3c 38 00 74 08 4c 89 f7 e8 fc 1d e0 fe 49 8b 1e 48 83 c5 68
> RSP: 0018:ffffc90002dcfb28 EFLAGS: 00010202
> RAX: 000000000000000d RBX: 1ffff920005b9f79 RCX: ffff88801efa5a00
> RDX: 0000000000000000 RSI: ffffc90002dcfbc0 RDI: ffff888031c9bc00
> RBP: ffff88807eb938f8 R08: ffffffff831d82d9 R09: 0000000000000000
> R10: ffffc90002dcfae0 R11: fffff520005b9f5e R12: 0000000000000000
> R13: ffff888078c80000 R14: 0000000000000068 R15: dffffc0000000000
> FS:  0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020001740 CR3: 000000000e736000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:   03 4d 89                add    -0x77(%rbp),%ecx
>    3:   f7 42 80 3c 30 00 74    testl  $0x7400303c,-0x80(%rdx)
>    a:   08 4c 89 ef             or     %cl,-0x11(%rcx,%rcx,4)
>    e:   e8 22 1e e0 fe          call   0xfee01e35
>   13:   4c 89 64 24 10          mov    %r12,0x10(%rsp)
>   18:   49 8b 45 00             mov    0x0(%r13),%rax
>   1c:   49 89 c4                mov    %rax,%r12
>   1f:   4c 8d 70 68             lea    0x68(%rax),%r14
>   23:   4c 89 f0                mov    %r14,%rax
>   26:   48 c1 e8 03             shr    $0x3,%rax
> * 2a:   42 80 3c 38 00          cmpb   $0x0,(%rax,%r15,1) <-- trapping instruction
>   2f:   74 08                   je     0x39
>   31:   4c 89 f7                mov    %r14,%rdi
>   34:   e8 fc 1d e0 fe          call   0xfee01e35
>   39:   49 8b 1e                mov    (%r14),%rbx
>   3c:   48 83 c5 68             add    $0x68,%rbp
>
>

OOPS broke O_TMPFILE.

#syz test: https://github.com/amir73il/linux ovl_real_file

Thanks,
Amir.