From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Dmitry Vyukov <dvyukov@google.com>,
syzbot <syzbot+b7c3ba8cdc2f6cf83c21@syzkaller.appspotmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>
Cc: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [kernel?] KCSAN: data-race in __fput / __tty_hangup (4)
Date: Sun, 23 Apr 2023 22:28:58 +0900 [thread overview]
Message-ID: <6bec279c-07b3-d6f1-0860-4d6b136a2025@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <CACT4Y+bj7jCOjGV5jCUPzN5zjgdHxRn9vkwQEBuPWVzMbMCnXw@mail.gmail.com>
On 2023/04/21 17:21, Dmitry Vyukov wrote:
> On Fri, 21 Apr 2023 at 10:18, syzbot
> <syzbot+b7c3ba8cdc2f6cf83c21@syzkaller.appspotmail.com> wrote:
>>
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: fcd476ea6a88 Merge tag 'urgent-rcu.2023.03.28a' of git://g..
>> git tree: upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=146618b9c80000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=f7350c77b8056a38
>> dashboard link: https://syzkaller.appspot.com/bug?extid=b7c3ba8cdc2f6cf83c21
>> compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
>>
>> Unfortunately, I don't have any reproducer for this issue yet.
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/f3d8ce4faab0/disk-fcd476ea.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/fc53d9dee279/vmlinux-fcd476ea.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/22ad755d39b2/bzImage-fcd476ea.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+b7c3ba8cdc2f6cf83c21@syzkaller.appspotmail.com
>
> If I am reading this correctly, this race can lead to NULL derefs
> among other things.
> hung_up_tty_fops does not have splice_read, while other fops have.
>
> So the following code in splice can execute NULL callback:
>
> if (unlikely(!in->f_op->splice_read))
> return warn_unsupported(in, "read");
> return in->f_op->splice_read(in, ppos, pipe, len, flags);
Hmm, it seems to me that we need multiple patches (which would become too big to
backport) for fixing this bug.
First step (which Dmitry mentioned) is to avoid potential NULL pointer dereferences
caused by
if (!f_op->$callbackname) {
return error;
}
return f_op->$callbackname($args);
pattern, for the next step will touch too many locations to change all at once whereas
the first step could be handled by implementing dummy function for all missing $callbackname.
Next step is to convert from
if (!f_op->$callbackname) {
return error;
}
return f_op->$callbackname($args);
to
fn = READ_ONCE(f_op->$callbackname);
if (!fn) {
return error;
}
return fn($args);
pattern.
Last step is to silence KCSAN by wrapping READ_ONCE()/WRITE_ONCE() using data_race() macro.
Each data_race() usage wants a comment, thus would want a macro if possible...
next prev parent reply other threads:[~2023-04-23 13:29 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-21 8:18 [syzbot] [kernel?] KCSAN: data-race in __fput / __tty_hangup (4) syzbot
2023-04-21 8:21 ` Dmitry Vyukov
2023-04-21 15:12 ` Tetsuo Handa
2023-04-21 16:02 ` Tetsuo Handa
2023-04-23 23:34 ` Al Viro
2023-04-23 23:55 ` Tetsuo Handa
2023-04-24 0:44 ` Al Viro
2023-04-24 1:09 ` Tetsuo Handa
2023-04-25 14:47 ` Tetsuo Handa
2023-04-25 16:03 ` Al Viro
2023-04-25 22:09 ` Tetsuo Handa
2023-04-26 11:05 ` [PATCH] tty: tty_io: remove hung_up_tty_fops Tetsuo Handa
2023-04-28 16:27 ` Nathan Chancellor
2023-04-28 16:41 ` Tetsuo Handa
2023-04-28 17:11 ` Al Viro
2023-04-29 10:43 ` Tetsuo Handa
2023-04-28 17:31 ` Greg Kroah-Hartman
2023-04-29 15:21 ` Guenter Roeck
2023-05-01 18:42 ` Geert Uytterhoeven
2023-05-14 1:02 ` [PATCH v2] " Tetsuo Handa
2023-05-30 10:44 ` Greg Kroah-Hartman
2023-05-30 11:57 ` Tetsuo Handa
2023-05-30 12:51 ` Greg Kroah-Hartman
2024-04-27 6:20 ` [PATCH v3] " Tetsuo Handa
2024-04-27 19:02 ` Linus Torvalds
2024-04-28 10:19 ` Tetsuo Handa
2024-04-28 18:50 ` Linus Torvalds
2024-04-29 13:55 ` Marco Elver
2024-04-29 15:38 ` Linus Torvalds
2024-05-01 18:45 ` Paul E. McKenney
2024-05-01 18:56 ` Linus Torvalds
2024-05-01 19:02 ` Paul E. McKenney
2024-05-01 20:14 ` Marco Elver
2024-05-01 21:06 ` Linus Torvalds
2024-05-01 21:20 ` Linus Torvalds
2024-05-01 21:49 ` Paul E. McKenney
2024-05-01 22:32 ` Paul E. McKenney
2024-05-02 16:37 ` Boqun Feng
2024-05-03 23:59 ` Paul E. McKenney
2024-05-04 0:14 ` Linus Torvalds
2024-05-04 5:08 ` Paul E. McKenney
2024-05-04 17:50 ` Linus Torvalds
2024-05-04 18:18 ` Paul E. McKenney
2024-05-04 19:11 ` Linus Torvalds
2024-05-04 19:25 ` Linus Torvalds
2024-05-04 22:17 ` Paul E. McKenney
2024-05-04 22:04 ` Paul E. McKenney
2024-05-02 14:14 ` Marco Elver
2024-05-02 16:42 ` Tetsuo Handa
2024-05-02 17:20 ` Marco Elver
2024-05-02 17:29 ` Linus Torvalds
2024-05-02 18:14 ` Al Viro
2024-05-02 19:29 ` Marco Elver
2024-05-02 23:54 ` Tetsuo Handa
2024-05-03 1:12 ` Linus Torvalds
2023-04-23 13:28 ` Tetsuo Handa [this message]
2023-04-23 14:00 ` [syzbot] [kernel?] KCSAN: data-race in __fput / __tty_hangup (4) Greg Kroah-Hartman
2023-04-23 14:03 ` Greg Kroah-Hartman
2023-04-23 14:17 ` Tetsuo Handa
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