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Subject[PATCH] tty: n_gsm: restrict tty devices to attach
From
syzbot is reporting sleep in atomic context, for gsmld_write() is calling
con_write() with spinlock held and IRQs disabled.

Since n_gsm is designed to be used for serial port, reject attaching to
virtual consoles and PTY devices, by checking tty's device major/minor
numbers at gsmld_open().

Link: https://www.kernel.org/doc/html/v6.7/driver-api/tty/n_gsm.html
Reported-by: syzbot+06fa1063cca8163ea541@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=06fa1063cca8163ea541
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
drivers/tty/n_gsm.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 4036566febcb..14581483af78 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -3623,6 +3623,7 @@ static void gsmld_close(struct tty_struct *tty)
static int gsmld_open(struct tty_struct *tty)
{
struct gsm_mux *gsm;
+ int major;

if (!capable(CAP_NET_ADMIN))
return -EPERM;
@@ -3630,6 +3631,17 @@ static int gsmld_open(struct tty_struct *tty)
if (tty->ops->write == NULL)
return -EINVAL;

+ major = tty->driver->major;
+ /* Reject Virtual consoles */
+ if (major == 4 && tty->driver->minor_start == 1)
+ return -EINVAL;
+ /* Reject Unix98 PTY masters/slaves */
+ if (major >= 128 && major <= 143)
+ return -EINVAL;
+ /* Reject BSD PTY masters/slaves */
+ if (major >= 2 && major <= 3)
+ return -EINVAL;
+
/* Attach our ldisc data */
gsm = gsm_alloc_mux();
if (gsm == NULL)
--
2.18.4


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