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authorNguyen Dinh Phi <phind.uet@gmail.com>2021-08-23 08:06:41 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-08-26 14:51:38 +0200
commitbb2853a6a421a052268eee00fd5d3f6b3504b2b1 (patch)
tree4d85d35bb4f84942eec19f5d22757f10c14846f3
parent74d2fb7e708433b7397d9647ea7ec1cbcb0ae379 (diff)
tty: Fix data race between tiocsti() and flush_to_ldisc()
The ops->receive_buf() may be accessed concurrently from these two functions. If the driver flushes data to the line discipline receive_buf() method while tiocsti() is waiting for the ops->receive_buf() to finish its work, the data race will happen. For example: tty_ioctl |tty_ldisc_receive_buf ->tioctsi | ->tty_port_default_receive_buf | ->tty_ldisc_receive_buf ->hci_uart_tty_receive | ->hci_uart_tty_receive ->h4_recv | ->h4_recv In this case, the h4 receive buffer will be overwritten by the latecomer, and we will lost the data. Hence, change tioctsi() function to use the exclusive lock interface from tty_buffer to avoid the data race. Reported-by: syzbot+97388eb9d31b997fe1d0@syzkaller.appspotmail.com Reviewed-by: Jiri Slaby <jirislaby@kernel.org> Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com> Link: https://lore.kernel.org/r/20210823000641.2082292-1-phind.uet@gmail.com Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/tty_io.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index e8532006e960..6616d4a0d41d 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2290,8 +2290,6 @@ static int tty_fasync(int fd, struct file *filp, int on)
* Locking:
* Called functions take tty_ldiscs_lock
* current->signal->tty check is safe without locks
- *
- * FIXME: may race normal receive processing
*/
static int tiocsti(struct tty_struct *tty, char __user *p)
@@ -2307,8 +2305,10 @@ static int tiocsti(struct tty_struct *tty, char __user *p)
ld = tty_ldisc_ref_wait(tty);
if (!ld)
return -EIO;
+ tty_buffer_lock_exclusive(tty->port);
if (ld->ops->receive_buf)
ld->ops->receive_buf(tty, &ch, &mbz, 1);
+ tty_buffer_unlock_exclusive(tty->port);
tty_ldisc_deref(ld);
return 0;
}