netdev - Re: [syzbot] [mptcp?] general protection fault in proc

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Message-ID: <20250104200913.GG1977892@ZenIV>
Date: Sat, 4 Jan 2025 20:09:13 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Matthieu Baerts <matttbe@...nel.org>, davem@...emloft.net,
	geliang@...nel.org, horms@...nel.org, kuba@...nel.org,
	linux-kernel@...r.kernel.org, martineau@...nel.org,
	mptcp@...ts.linux.dev, netdev@...r.kernel.org, pabeni@...hat.com,
	syzkaller-bugs@...glegroups.com,
	syzbot <syzbot+e364f774c6f57f2c86d1@...kaller.appspotmail.com>
Subject: Re: [syzbot] [mptcp?] general protection fault in proc_scheduler

On Sat, Jan 04, 2025 at 07:53:22PM +0100, Eric Dumazet wrote:
> I do think this is a bug in process accounting, not in networking.
> 
> It might make sense to output a record on a regular file, but probably
> not on any other files.
> 
> diff --git a/kernel/acct.c b/kernel/acct.c
> index 179848ad33e978a557ce695a0d6020aa169177c6..a211305cb930f6860d02de7f45ebd260ae03a604
> 100644
> --- a/kernel/acct.c
> +++ b/kernel/acct.c
> @@ -495,6 +495,9 @@ static void do_acct_process(struct bsd_acct_struct *acct)
>         const struct cred *orig_cred;
>         struct file *file = acct->file;
> 
> +       if (S_ISREG(file_inode(file)->i_mode))
> +               return;

Wait, what?  OK, that will stop attempts to write there - or to any
other regular file.

If you modify that to
	if (!S_ISREG(...))
you seem to have intended, it won't break the normal behaviour but it
won't help with sysctls.