From: Greg KH <gregkh@linuxfoundation.org>
To: Jeongjun Park <aha310510@gmail.com>
Cc: jirislaby@kernel.org, linux-kernel@vger.kernel.org,
linux-serial@vger.kernel.org
Subject: Re: [PATCH] n_tty: fix data race in n_tty_poll()
Date: Wed, 21 May 2025 13:27:06 +0200 [thread overview]
Message-ID: <2025052123-landmark-capitol-effb@gregkh> (raw)
In-Reply-To: <20250510163828.21963-1-aha310510@gmail.com>
On Sun, May 11, 2025 at 01:38:27AM +0900, Jeongjun Park wrote:
> I found data-race in my fuzzer:
>
> ==================================================================
> BUG: KCSAN: data-race in n_tty_poll / tty_set_termios
>
> read to 0xffff8880116b4d14 of 4 bytes by task 5443 on cpu 0:
> n_tty_poll+0xa4/0x4c0 drivers/tty/n_tty.c:2452
> tty_poll+0x8f/0x100 drivers/tty/tty_io.c:2208
> vfs_poll include/linux/poll.h:82 [inline]
> select_poll_one fs/select.c:480 [inline]
> do_select+0x95f/0x1030 fs/select.c:536
> core_sys_select+0x284/0x6d0 fs/select.c:677
> ....
>
> write to 0xffff8880116b4d08 of 44 bytes by task 14547 on cpu 1:
> tty_set_termios+0xf9/0x500 drivers/tty/tty_ioctl.c:339
> set_termios.part.0+0x3bc/0x4d0 drivers/tty/tty_ioctl.c:520
> set_termios drivers/tty/tty_ioctl.c:454 [inline]
> tty_mode_ioctl+0x2db/0xa00 drivers/tty/tty_ioctl.c:807
> n_tty_ioctl_helper+0x4e/0x230 drivers/tty/tty_ioctl.c:986
> n_tty_ioctl+0x67/0x230 drivers/tty/n_tty.c:2509
> ....
> ==================================================================
>
> In n_tty_poll() we are doing a read on tty->termios but we are missing
> rwsem lock, which causes a concurrency problem. To fix this, we need to
> add rwsem lock at the appropriate location.
Does this "concurrency problem" actually cause a real issue?
As the tools point out, your change will not work as you will have a
locking deadlock, which makes me wonder how you tested it?
thanks,
greg k-h
prev parent reply other threads:[~2025-05-21 11:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-05-10 16:38 [PATCH] n_tty: fix data race in n_tty_poll() Jeongjun Park
2025-05-12 6:21 ` kernel test robot
2025-05-21 11:27 ` Greg KH [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=2025052123-landmark-capitol-effb@gregkh \
--to=gregkh@linuxfoundation.org \
--cc=aha310510@gmail.com \
--cc=jirislaby@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-serial@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.