| Message ID | 42d17017-1d30-4c54-9c28-9d9ba2494e07@I-love.SAKURA.ne.jp |
|---|---|
| State | New |
| Headers | show |
| Series | tty: n_gsm: restrict tty devices to attach | expand |
On Wed, Jan 24, 2024 at 07:06:04PM +0900, Tetsuo Handa wrote: > 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; That is a lot of hard-coded magic numbers, why aren't these defined anywhere? But really, this is only for fuzz testers, why can't they just not ever bind this to a console? Why do we have to have these checks in the kernel to prevent userspace from doing dumb things that no real userspace will ever do? thanks, greg k-h
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)
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(+)