linux-kernel - Re: [syzbot] [fs?] kernel BUG in may

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Message-ID: <5u3utx4wgzscgspbcpqhaj75gpg43gcmjnxfhbrjrgv6j6af3a@pbsz3qyoa2wk>
Date: Wed, 2 Apr 2025 23:02:09 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: syzbot <syzbot+5d8e79d323a13aa0b248@...kaller.appspotmail.com>
Cc: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [syzbot] [fs?] kernel BUG in may_open

On Wed, Apr 02, 2025 at 06:46:27AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    08733088b566 Merge tag 'rust-fixes-6.15-merge' of git://gi..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=10c8a178580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=acce2ca43d1e8c46
> dashboard link: https://syzkaller.appspot.com/bug?extid=5d8e79d323a13aa0b248
> 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=15bb094c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12c2b7b0580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/2ec0ad16833c/disk-08733088.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/aaa58ee04595/vmlinux-08733088.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9799f5b55d91/bzImage-08733088.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+5d8e79d323a13aa0b248@...kaller.appspotmail.com
> 
> VFS_BUG_ON_INODE(1) encountered for inode ffff888148c44000
> ------------[ cut here ]------------
> kernel BUG at fs/namei.c:3432!
> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 0 UID: 0 PID: 5828 Comm: syz-executor329 Not tainted 6.14.0-syzkaller-11270-g08733088b566 #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> RIP: 0010:may_open+0x450/0x460 fs/namei.c:3432
> Code: 38 c1 0f 8c 95 fe ff ff 48 89 df e8 aa 3c eb ff e9 88 fe ff ff e8 10 b3 84 ff 4c 89 ef 48 c7 c6 c0 f6 58 8c e8 81 21 05 00 90 <0f> 0b 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90
> RSP: 0018:ffffc90003ce78d8 EFLAGS: 00010246
> RAX: 000000000000003a RBX: 00000000000fffff RCX: 8d133bf8e6cb7a00
> RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
> RBP: ffffffff8ee96300 R08: ffffffff81a29bdc R09: 1ffff9200079ceb8
> R10: dffffc0000000000 R11: fffff5200079ceb9 R12: 0000000000000006
> R13: ffff888148c44000 R14: dffffc0000000000 R15: ffffc90003ce7ba0
> FS:  0000555582428380(0000) GS:ffff888124fe2000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000056466efce608 CR3: 0000000033c36000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  do_open fs/namei.c:3843 [inline]
>  path_openat+0x2b39/0x35d0 fs/namei.c:4004
>  do_filp_open+0x284/0x4e0 fs/namei.c:4031
>  do_sys_openat2+0x12b/0x1d0 fs/open.c:1429
>  do_sys_open fs/open.c:1444 [inline]
>  __do_sys_openat fs/open.c:1460 [inline]
>  __se_sys_openat fs/open.c:1455 [inline]
>  __x64_sys_openat+0x249/0x2a0 fs/open.c:1455
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f

This is issuing open on bpf:

bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_DEVMAP, key_size=4, value_size=4, max_entries=3, map_flags=0,
inner_map_fd=-1, map_name="", map_ifindex=0, btf_fd=-1, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 3
openat(AT_FDCWD, "/proc/self/fd/3", O_RDWR) = ?
+++ killed by SIGSEGV +++

I verified i_mode & S_ISFMT is 0.

I don't know what expectation is, should this be some special dev
instead?