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From 8a9cce994f0c37c1b4dfc313a1b01fb009c55d01 Mon Sep 17 00:00:00 2001
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From: Julien Thierry <jthierry@redhat.com>
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Date: Thu, 21 Jan 2021 14:41:40 +0100
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Subject: [PATCH] [tty] Fix ->pgrp locking in tiocspgrp()
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Kernels:
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3.10.0-1160.el7
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3.10.0-1160.2.1.el7
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3.10.0-1160.2.2.el7
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3.10.0-1160.6.1.el7
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3.10.0-1160.11.1.el7
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3.10.0-1160.15.1.el7
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Changes since last build:
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arches: x86_64 ppc64le
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tty_io.o: changed function: tty_ioctl
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---------------------------
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Modifications:
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None
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commit ba0ec80fb32a3ca6e15d51ddcb54c1095f04cf2a
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Author: Chris von Recklinghausen <crecklin@redhat.com>
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Date: Wed Jan 6 19:26:01 2021 -0500
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[tty] Fix ->pgrp locking in tiocspgrp()
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Message-id: <20210106192601.11675-1-crecklin@redhat.com>
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Patchwork-id: 10200
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Patchwork-instance: patchwork-private
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O-Subject: [kernel team] [RHEL 7.9.Z bz1908193 CVE-2020-29661 PATCH] tty: Fix ->pgrp locking in tiocspgrp()
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Bugzilla: 1908193
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CVE: CVE-2020-29661
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RH-Acked-by: Oleg Nesterov <oleg@redhat.com>
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RH-Acked-by: Waiman Long <longman@redhat.com>
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From: Jann Horn <jannh@google.com>
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1908193
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Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=34103731
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CVE: CVE-2020-29661
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Upstream Status: linux
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Tested: CKI https://beaker.engineering.redhat.com/jobs/?jobsearch-0.table=Whiteboard&jobsearch-0.operation=contains&jobsearch-0.value=cki%40gitlab%3A620704
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bug has no reproducer
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Conflicts: tiocspgrp is defined in drivers/tty/tty_io.c in rhel7 so make
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change there.
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drop changes to drivers/tty/tty_jobctrl.c
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tiocspgrp() takes two tty_struct pointers: One to the tty that userspace
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passed to ioctl() (`tty`) and one to the TTY being changed (`real_tty`).
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These pointers are different when ioctl() is called with a master fd.
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To properly lock real_tty->pgrp, we must take real_tty->ctrl_lock.
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This bug makes it possible for racing ioctl(TIOCSPGRP, ...) calls on
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both sides of a PTY pair to corrupt the refcount of `struct pid`,
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leading to use-after-free errors.
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Fixes: 47f86834bbd4 ("redo locking of tty->pgrp")
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CC: stable@kernel.org
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Signed-off-by: Jann Horn <jannh@google.com>
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Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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(cherry picked from commit 54ffccbf053b5b6ca4f6e45094b942fab92a25fc)
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Conflicts:
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drivers/tty/tty_jobctrl.c
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Signed-off-by: Chris von Recklinghausen <crecklin@redhat.com>
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Signed-off-by: Augusto Caringi <acaringi@redhat.com>
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Signed-off-by: Julien Thierry <jthierry@redhat.com>
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---
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drivers/tty/tty_io.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
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index c6e277aae06..713e1ad5c09 100644
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--- a/drivers/tty/tty_io.c
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+++ b/drivers/tty/tty_io.c
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@@ -2542,10 +2542,10 @@ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t
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if (session_of_pgrp(pgrp) != task_session(current))
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goto out_unlock;
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retval = 0;
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- spin_lock_irqsave(&tty->ctrl_lock, flags);
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+ spin_lock_irqsave(&real_tty->ctrl_lock, flags);
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put_pid(real_tty->pgrp);
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real_tty->pgrp = get_pid(pgrp);
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- spin_unlock_irqrestore(&tty->ctrl_lock, flags);
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+ spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
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out_unlock:
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rcu_read_unlock();
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return retval;
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--
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2.25.4
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