From: Linus Torvalds torvalds@linux-foundation.org
[ Upstream commit 6bd23e0c2bb6c65d4f5754d1456bc9a4427fc59b ]
... and use it to limit the virtual terminals to just N_TTY. They are kind of special, and in particular, the "con_write()" routine violates the "writes cannot sleep" rule that some ldiscs rely on.
This avoids the
BUG: sleeping function called from invalid context at kernel/printk/printk.c:2659
when N_GSM has been attached to a virtual console, and gsmld_write() calls con_write() while holding a spinlock, and con_write() then tries to get the console lock.
Tested-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Cc: Jiri Slaby jirislaby@kernel.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Daniel Starke daniel.starke@siemens.com Reported-by: syzbot syzbot+dbac96d8e73b61aa559c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=dbac96d8e73b61aa559c Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Link: https://lore.kernel.org/r/20240423163339.59780-1-torvalds@linux-foundation.o... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/tty_ldisc.c | 6 ++++++ drivers/tty/vt/vt.c | 10 ++++++++++ include/linux/tty_driver.h | 8 ++++++++ 3 files changed, 24 insertions(+)
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 3f68e213df1f7..d80e9d4c974b4 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -545,6 +545,12 @@ int tty_set_ldisc(struct tty_struct *tty, int disc) goto out; }
+ if (tty->ops->ldisc_ok) { + retval = tty->ops->ldisc_ok(tty, disc); + if (retval) + goto out; + } + old_ldisc = tty->ldisc;
/* Shutdown the old discipline. */ diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 52e6ca1ba21df..09126aed97bc1 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -3396,6 +3396,15 @@ static void con_cleanup(struct tty_struct *tty) tty_port_put(&vc->port); }
+/* + * We can't deal with anything but the N_TTY ldisc, + * because we can sleep in our write() routine. + */ +static int con_ldisc_ok(struct tty_struct *tty, int ldisc) +{ + return ldisc == N_TTY ? 0 : -EINVAL; +} + static int default_color = 7; /* white */ static int default_italic_color = 2; // green (ASCII) static int default_underline_color = 3; // cyan (ASCII) @@ -3515,6 +3524,7 @@ static const struct tty_operations con_ops = { .resize = vt_resize, .shutdown = con_shutdown, .cleanup = con_cleanup, + .ldisc_ok = con_ldisc_ok, };
static struct cdev vc0_cdev; diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h index 7372124fbf90b..dd4b31ce6d5d4 100644 --- a/include/linux/tty_driver.h +++ b/include/linux/tty_driver.h @@ -154,6 +154,13 @@ struct serial_struct; * * Optional. Called under the @tty->termios_rwsem. May sleep. * + * @ldisc_ok: ``int ()(struct tty_struct *tty, int ldisc)`` + * + * This routine allows the @tty driver to decide if it can deal + * with a particular @ldisc. + * + * Optional. Called under the @tty->ldisc_sem and @tty->termios_rwsem. + * * @set_ldisc: ``void ()(struct tty_struct *tty)`` * * This routine allows the @tty driver to be notified when the device's @@ -372,6 +379,7 @@ struct tty_operations { void (*hangup)(struct tty_struct *tty); int (*break_ctl)(struct tty_struct *tty, int state); void (*flush_buffer)(struct tty_struct *tty); + int (*ldisc_ok)(struct tty_struct *tty, int ldisc); void (*set_ldisc)(struct tty_struct *tty); void (*wait_until_sent)(struct tty_struct *tty, int timeout); void (*send_xchar)(struct tty_struct *tty, u8 ch);