Re: [syzbot] [mptcp?] general protection fault in proc_scheduler

Eric Dumazet
2025-01-02T15:21:56Z

On Thu, Jan 2, 2025 at 3:12 PM syzbot
<syzbot+e364f774c6f57f2c86d1@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: ccb98ccef0e5 Merge tag 'platform-drivers-x86-v6.13-4' of g..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=128f6ac4580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=86dd15278dbfe19f
> dashboard link: https://syzkaller.appspot.com/bug?extid=e364f774c6f57f2c86d1
> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1245eaf8580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/d24eb225cff7/disk-ccb98cce.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/dd81532f8240/vmlinux-ccb98cce.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/18b08e4bbf40/bzImage-ccb98cce.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e364f774c6f57f2c86d1@syzkaller.appspotmail.com
>
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
> CPU: 1 UID: 0 PID: 5924 Comm: syz-executor Not tainted 6.13.0-rc5-syzkaller-00004-gccb98ccef0e5 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> RIP: 0010:proc_scheduler+0xc6/0x3c0 net/mptcp/ctrl.c:125
> Code: 03 42 80 3c 38 00 0f 85 fe 02 00 00 4d 8b a4 24 08 09 00 00 48 b8 00 00 00 00 00 fc ff df 49 8d 7c 24 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 cc 02 00 00 4d 8b 7c 24 28 48 8d 84 24 c8 00 00
> RSP: 0018:ffffc900034774e8 EFLAGS: 00010206
>
> RAX: dffffc0000000000 RBX: 1ffff9200068ee9e RCX: ffffc90003477620
> RDX: 0000000000000005 RSI: ffffffff8b08f91e RDI: 0000000000000028
> RBP: 0000000000000001 R08: ffffc90003477710 R09: 0000000000000040
> R10: 0000000000000040 R11: 00000000726f7475 R12: 0000000000000000
> R13: ffffc90003477620 R14: ffffc90003477710 R15: dffffc0000000000
> FS: 0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fee3cd452d8 CR3: 000000007d116000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> proc_sys_call_handler+0x403/0x5d0 fs/proc/proc_sysctl.c:601
> __kernel_write_iter+0x318/0xa80 fs/read_write.c:612
> __kernel_write+0xf6/0x140 fs/read_write.c:632
> do_acct_process+0xcb0/0x14a0 kernel/acct.c:539
> acct_pin_kill+0x2d/0x100 kernel/acct.c:192
> pin_kill+0x194/0x7c0 fs/fs_pin.c:44
> mnt_pin_kill+0x61/0x1e0 fs/fs_pin.c:81
> cleanup_mnt+0x3ac/0x450 fs/namespace.c:1366
> task_work_run+0x14e/0x250 kernel/task_work.c:239
> exit_task_work include/linux/task_work.h:43 [inline]
> do_exit+0xad8/0x2d70 kernel/exit.c:938
> do_group_exit+0xd3/0x2a0 kernel/exit.c:1087
> get_signal+0x2576/0x2610 kernel/signal.c:3017
> arch_do_signal_or_restart+0x90/0x7e0 arch/x86/kernel/signal.c:337
> exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
> exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
> __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
> syscall_exit_to_user_mode+0x150/0x2a0 kernel/entry/common.c:218
> do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fee3cb87a6a
> Code: Unable to access opcode bytes at 0x7fee3cb87a40.
> RSP: 002b:00007fffcccac688 EFLAGS: 00000202 ORIG_RAX: 0000000000000037
> RAX: 0000000000000000 RBX: 00007fffcccac710 RCX: 00007fee3cb87a6a
> RDX: 0000000000000041 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 0000000000000003 R08: 00007fffcccac6ac R09: 00007fffcccacac7
> R10: 00007fffcccac710 R11: 0000000000000202 R12: 00007fee3cd49500
> R13: 00007fffcccac6ac R14: 0000000000000000 R15: 00007fee3cd4b000
> </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:proc_scheduler+0xc6/0x3c0 net/mptcp/ctrl.c:125
> Code: 03 42 80 3c 38 00 0f 85 fe 02 00 00 4d 8b a4 24 08 09 00 00 48 b8 00 00 00 00 00 fc ff df 49 8d 7c 24 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 cc 02 00 00 4d 8b 7c 24 28 48 8d 84 24 c8 00 00
> RSP: 0018:ffffc900034774e8 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: 1ffff9200068ee9e RCX: ffffc90003477620
> RDX: 0000000000000005 RSI: ffffffff8b08f91e RDI: 0000000000000028
> RBP: 0000000000000001 R08: ffffc90003477710 R09: 0000000000000040
> R10: 0000000000000040 R11: 00000000726f7475 R12: 0000000000000000
> R13: ffffc90003477620 R14: ffffc90003477710 R15: dffffc0000000000
> FS: 0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fee3cd452d8 CR3: 000000007d116000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess), 1 bytes skipped:
> 0: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1)
> 5: 0f 85 fe 02 00 00 jne 0x309
> b: 4d 8b a4 24 08 09 00 mov 0x908(%r12),%r12
> 12: 00
> 13: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
> 1a: fc ff df
> 1d: 49 8d 7c 24 28 lea 0x28(%r12),%rdi
> 22: 48 89 fa mov %rdi,%rdx
> 25: 48 c1 ea 03 shr $0x3,%rdx
> * 29: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction
> 2d: 0f 85 cc 02 00 00 jne 0x2ff
> 33: 4d 8b 7c 24 28 mov 0x28(%r12),%r15
> 38: 48 rex.W
> 39: 8d .byte 0x8d
> 3a: 84 24 c8 test %ah,(%rax,%rcx,8)
>
>
> ---
> This report is generated by a bot. It may contain errors.
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>
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I thought acct(2) was only allowing regular files.

acct_on() indeed has :

if (!S_ISREG(file_inode(file)->i_mode)) {
kfree(acct);
filp_close(file, NULL);
return -EACCES;
}

It seems there are other ways to call do_acct_process() targeting a sysfs file ?