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authorJann Horn <jannh@google.com>2020-12-03 04:25:04 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-12-04 19:38:48 +0300
commit54ffccbf053b5b6ca4f6e45094b942fab92a25fc (patch)
treeb30e76730582ec6960a35741dea3023040afbaf0 /drivers/tty
parent418baf2c28f3473039f2f7377760bd8f6897ae18 (diff)
downloadlinux-54ffccbf053b5b6ca4f6e45094b942fab92a25fc.tar.xz
tty: Fix ->pgrp locking in tiocspgrp()
tiocspgrp() takes two tty_struct pointers: One to the tty that userspace passed to ioctl() (`tty`) and one to the TTY being changed (`real_tty`). These pointers are different when ioctl() is called with a master fd. To properly lock real_tty->pgrp, we must take real_tty->ctrl_lock. This bug makes it possible for racing ioctl(TIOCSPGRP, ...) calls on both sides of a PTY pair to corrupt the refcount of `struct pid`, leading to use-after-free errors. Fixes: 47f86834bbd4 ("redo locking of tty->pgrp") CC: stable@kernel.org Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: Jiri Slaby <jirislaby@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/tty_jobctrl.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/tty/tty_jobctrl.c b/drivers/tty/tty_jobctrl.c
index 28a23a0fef21..baadeea4a289 100644
--- a/drivers/tty/tty_jobctrl.c
+++ b/drivers/tty/tty_jobctrl.c
@@ -494,10 +494,10 @@ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t
if (session_of_pgrp(pgrp) != task_session(current))
goto out_unlock;
retval = 0;
- spin_lock_irq(&tty->ctrl_lock);
+ spin_lock_irq(&real_tty->ctrl_lock);
put_pid(real_tty->pgrp);
real_tty->pgrp = get_pid(pgrp);
- spin_unlock_irq(&tty->ctrl_lock);
+ spin_unlock_irq(&real_tty->ctrl_lock);
out_unlock:
rcu_read_unlock();
return retval;