From 8a9cce994f0c37c1b4dfc313a1b01fb009c55d01 Mon Sep 17 00:00:00 2001
From: Julien Thierry <jthierry@redhat.com>
Date: Thu, 21 Jan 2021 14:41:40 +0100
Subject: [PATCH] [tty] Fix ->pgrp locking in tiocspgrp()
Kernels:
3.10.0-1160.el7
3.10.0-1160.2.1.el7
3.10.0-1160.2.2.el7
3.10.0-1160.6.1.el7
3.10.0-1160.11.1.el7
3.10.0-1160.15.1.el7
Changes since last build:
arches: x86_64 ppc64le
tty_io.o: changed function: tty_ioctl
---------------------------
Modifications:
None
commit ba0ec80fb32a3ca6e15d51ddcb54c1095f04cf2a
Author: Chris von Recklinghausen <crecklin@redhat.com>
Date: Wed Jan 6 19:26:01 2021 -0500
[tty] Fix ->pgrp locking in tiocspgrp()
Message-id: <20210106192601.11675-1-crecklin@redhat.com>
Patchwork-id: 10200
Patchwork-instance: patchwork-private
O-Subject: [kernel team] [RHEL 7.9.Z bz1908193 CVE-2020-29661 PATCH] tty: Fix ->pgrp locking in tiocspgrp()
Bugzilla: 1908193
CVE: CVE-2020-29661
RH-Acked-by: Oleg Nesterov <oleg@redhat.com>
RH-Acked-by: Waiman Long <longman@redhat.com>
From: Jann Horn <jannh@google.com>
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1908193
Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=34103731
CVE: CVE-2020-29661
Upstream Status: linux
Tested: CKI https://beaker.engineering.redhat.com/jobs/?jobsearch-0.table=Whiteboard&jobsearch-0.operation=contains&jobsearch-0.value=cki%40gitlab%3A620704
bug has no reproducer
Conflicts: tiocspgrp is defined in drivers/tty/tty_io.c in rhel7 so make
change there.
drop changes to drivers/tty/tty_jobctrl.c
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>
(cherry picked from commit 54ffccbf053b5b6ca4f6e45094b942fab92a25fc)
Conflicts:
drivers/tty/tty_jobctrl.c
Signed-off-by: Chris von Recklinghausen <crecklin@redhat.com>
Signed-off-by: Augusto Caringi <acaringi@redhat.com>
Signed-off-by: Julien Thierry <jthierry@redhat.com>
---
drivers/tty/tty_io.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index c6e277aae06..713e1ad5c09 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2542,10 +2542,10 @@ 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_irqsave(&tty->ctrl_lock, flags);
+ spin_lock_irqsave(&real_tty->ctrl_lock, flags);
put_pid(real_tty->pgrp);
real_tty->pgrp = get_pid(pgrp);
- spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+ spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
out_unlock:
rcu_read_unlock();
return retval;
--
2.25.4