From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
syzbot+5f47a8cea6a12b77a876@syzkaller.appspotmail.com,
Marco Elver <elver@google.com>, Max Filippov <jcmvbkbc@gmail.com>,
David Sterba <dsterba@suse.com>,
Bhaskar Chowdhury <unixbhaskar@gmail.com>,
nick black <dankamongmen@gmail.com>,
Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
Subject: [PATCH (resend)] tty: n_hdlc: make n_hdlc_tty_wakeup() asynchronous
Date: Wed, 15 Dec 2021 20:52:40 +0900 [thread overview]
Message-ID: <40de8b7e-a3be-4486-4e33-1b1d1da452f8@i-love.sakura.ne.jp> (raw)
In-Reply-To: <c9c18419-ff32-6c87-195a-923ebb28c466@i-love.sakura.ne.jp>
syzbot is reporting that an unprivileged user who logged in from tty
console can crash the system using a reproducer shown below [1], for
n_hdlc_tty_wakeup() is synchronously calling n_hdlc_send_frames().
----------
#include <sys/ioctl.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
const int disc = 0xd;
ioctl(1, TIOCSETD, &disc);
while (1) {
ioctl(1, TCXONC, 0);
write(1, "", 1);
ioctl(1, TCXONC, 1); /* Kernel panic - not syncing: scheduling while atomic */
}
}
----------
Linus suspected that "struct tty_ldisc"->ops->write_wakeup() must not
sleep, and Jiri confirmed it from include/linux/tty_ldisc.h. Thus, defer
n_hdlc_send_frames() from n_hdlc_tty_wakeup() to a WQ context like
net/nfc/nci/uart.c does.
Link: https://syzkaller.appspot.com/bug?extid=5f47a8cea6a12b77a876 [1]
Reported-by: syzbot <syzbot+5f47a8cea6a12b77a876@syzkaller.appspotmail.com>
Analyzed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Confirmed-by: Jiri Slaby <jirislaby@kernel.org>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
drivers/tty/n_hdlc.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
index 7e0884ecc74f..23ba1fc99df8 100644
--- a/drivers/tty/n_hdlc.c
+++ b/drivers/tty/n_hdlc.c
@@ -140,6 +140,8 @@ struct n_hdlc {
struct n_hdlc_buf_list rx_buf_list;
struct n_hdlc_buf_list tx_free_buf_list;
struct n_hdlc_buf_list rx_free_buf_list;
+ struct work_struct write_work;
+ struct tty_struct *tty_for_write_work;
};
/*
@@ -154,6 +156,7 @@ static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
/* Local functions */
static struct n_hdlc *n_hdlc_alloc(void);
+static void n_hdlc_tty_write_work(struct work_struct *work);
/* max frame size for memory allocations */
static int maxframe = 4096;
@@ -210,6 +213,8 @@ static void n_hdlc_tty_close(struct tty_struct *tty)
wake_up_interruptible(&tty->read_wait);
wake_up_interruptible(&tty->write_wait);
+ cancel_work_sync(&n_hdlc->write_work);
+
n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
@@ -241,6 +246,8 @@ static int n_hdlc_tty_open(struct tty_struct *tty)
return -ENFILE;
}
+ INIT_WORK(&n_hdlc->write_work, n_hdlc_tty_write_work);
+ n_hdlc->tty_for_write_work = tty;
tty->disc_data = n_hdlc;
tty->receive_room = 65536;
@@ -334,6 +341,20 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
goto check_again;
} /* end of n_hdlc_send_frames() */
+/**
+ * n_hdlc_tty_write_work - Asynchronous callback for transmit wakeup
+ * @work: pointer to work_struct
+ *
+ * Called when low level device driver can accept more send data.
+ */
+static void n_hdlc_tty_write_work(struct work_struct *work)
+{
+ struct n_hdlc *n_hdlc = container_of(work, struct n_hdlc, write_work);
+ struct tty_struct *tty = n_hdlc->tty_for_write_work;
+
+ n_hdlc_send_frames(n_hdlc, tty);
+} /* end of n_hdlc_tty_write_work() */
+
/**
* n_hdlc_tty_wakeup - Callback for transmit wakeup
* @tty: pointer to associated tty instance data
@@ -344,7 +365,7 @@ static void n_hdlc_tty_wakeup(struct tty_struct *tty)
{
struct n_hdlc *n_hdlc = tty->disc_data;
- n_hdlc_send_frames(n_hdlc, tty);
+ schedule_work(&n_hdlc->write_work);
} /* end of n_hdlc_tty_wakeup() */
/**
--
2.18.4
next prev parent reply other threads:[~2021-12-15 11:52 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-16 14:49 [PATCH] vt: Fix sleeping functions called from atomic context Fabio M. De Francesco
2021-11-16 14:58 ` Greg Kroah-Hartman
2021-11-16 15:35 ` Fabio M. De Francesco
2021-11-16 16:59 ` Greg Kroah-Hartman
2021-11-16 17:28 ` Fabio M. De Francesco
2021-11-17 8:23 ` Fabio M. De Francesco
2021-11-17 8:54 ` Greg Kroah-Hartman
2021-11-17 10:51 ` Tetsuo Handa
2021-11-18 8:31 ` Fabio M. De Francesco
2021-11-18 9:38 ` Fabio M. De Francesco
2021-11-18 12:14 ` Tetsuo Handa
2021-11-18 17:01 ` Fabio M. De Francesco
2021-11-19 14:55 ` [PATCH] tty: vt: make do_con_write() no-op if IRQ is disabled Tetsuo Handa
2021-12-01 13:40 ` Tetsuo Handa
2021-12-01 14:20 ` Greg Kroah-Hartman
2021-12-01 19:05 ` Linus Torvalds
2021-12-02 15:40 ` Tetsuo Handa
2021-12-02 18:35 ` Linus Torvalds
2021-12-03 5:03 ` Jiri Slaby
2021-12-03 11:00 ` Fabio M. De Francesco
2021-12-03 12:32 ` Tetsuo Handa
2021-12-03 14:51 ` Fabio M. De Francesco
2021-11-17 12:38 ` [PATCH] vt: Fix sleeping functions called from atomic context Fabio M. De Francesco
2021-11-17 1:55 ` Tetsuo Handa
2021-11-17 7:02 ` Fabio M. De Francesco
2021-12-06 11:44 ` [PATCH] tty: n_hdlc: make n_hdlc_tty_wakeup() asynchronous Tetsuo Handa
2021-12-06 18:07 ` Linus Torvalds
2021-12-09 13:18 ` Tetsuo Handa
2021-12-15 11:52 ` Tetsuo Handa [this message]
2021-12-06 19:06 ` Fabio M. De Francesco
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