linux-kernel - Re: [PATCH 1/1] Net: bcm.c: Remove Subtree Instead of Entry

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Message-Id: <20240809162141.139935-1-david.hunter.linux@gmail.com>
Date: Fri,  9 Aug 2024 12:21:41 -0400
From: David Hunter <david.hunter.linux@...il.com>
To: socketcan@...tkopp.net
Cc: davem@...emloft.net,
	david.hunter.linux@...il.com,
	edumazet@...gle.com,
	javier.carrasco.cruz@...il.com,
	kuba@...nel.org,
	linux-can@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	mkl@...gutronix.de,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	skhan@...uxfoundation.org
Subject: Re: [PATCH 1/1] Net: bcm.c: Remove Subtree Instead of Entry

Hello Oliver, 

> What did you do to trigger the warning? 

I am in the Linux Kernel Internship Program for the Linux Foundation. Our goal is to fix outstanding bugs with the kernel. I found the following bug on syzbot: 

https://syzkaller.appspot.com/bug?extid=df49d48077305d17519a

This specific link is for a separate issue that I will soon send a separate patch for; however, I found the bug for this patch after I switched the command parameter for panic_on_warn to 0. 

If you wish to reproduce the error, you can do the following steps: 
	1) compile and install a kernel with the config file from the link
	2) pass kernel paramter panic_on_warn=0
	3) build and run the C reproducer for the bug. 

As best as I can tell, the C reproducer simply made a system call that resulted in the bcm-can directry entry being deleted. I am still wrapping my head around the code (I am new to kernel programming), but here is the full stacktrace. 

156.449047][   T71] Call Trace:
[  156.450067][   T71]  <TASK>
[  156.451076][   T71]  ? show_regs+0x84/0x8b
[  156.452490][   T71]  ? __warn+0x150/0x29e
[  156.453754][   T71]  ? remove_proc_entry+0x335/0x385
[  156.456485][   T71]  ? report_bug+0x33d/0x431
[  156.457994][   T71]  ? remove_proc_entry+0x335/0x385
[  156.459845][   T71]  ? handle_bug+0x3d/0x66
[  156.461230][   T71]  ? exc_invalid_op+0x17/0x3e
[  156.462672][   T71]  ? asm_exc_invalid_op+0x1a/0x20
[  156.464282][   T71]  ? __warn_printk+0x26d/0x2aa
[  156.465759][   T71]  ? remove_proc_entry+0x335/0x385
[  156.467233][   T71]  ? remove_proc_entry+0x334/0x385
[  156.468821][   T71]  ? proc_readdir+0x11a/0x11a
[  156.470122][   T71]  ? __sanitizer_cov_trace_pc+0x1e/0x42
[  156.471697][   T71]  ? cgw_remove_all_jobs+0xa5/0x16f
[  156.474096][   T71]  canbcm_pernet_exit+0x73/0x79
[  156.476732][   T71]  ops_exit_list+0xf1/0x146
[  156.478358][   T71]  cleanup_net+0x333/0x570
[  156.479856][   T71]  ? setup_net+0x7ba/0x7ba
[  156.481479][   T71]  ? process_scheduled_works+0x652/0xbab
[  156.483592][   T71]  process_scheduled_works+0x7b8/0xbab
[  156.486039][   T71]  ? drain_workqueue+0x33b/0x33b
[  156.487841][   T71]  ? __sanitizer_cov_trace_pc+0x1e/0x42
[  156.489742][   T71]  ? move_linked_works+0x9f/0x108
[  156.491376][   T71]  worker_thread+0x5bd/0x6cc
[  156.492877][   T71]  ? rescuer_thread+0x64d/0x64d
[  156.494350][   T71]  kthread+0x30a/0x31e
[  156.495769][   T71]  ? kthread_complete_and_exit+0x35/0x35
[  156.497977][   T71]  ret_from_fork+0x34/0x6b
[  156.499734][   T71]  ? kthread_complete_and_exit+0x35/0x35
[  156.501494][   T71]  ret_from_fork_asm+0x11/0x20

> Removing this warning probably does not heal the root cause of the issue.

I would love to work on the root cause of the issue if at all possible. Do you think that the C reproducer went down an unlikely avenue, and therefore, further work is not needed, or do you think that this is an issue that requires some attention? 

I appreciate the response to my patch. I am learning a lot. 

Thanks, 
David