linux-kernel - [PATCH AUTOSEL 6.1 08/27] tty: allow TIOCSLCKTRMIOS with CAP_CHECKPOINT

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Message-ID: <20240128161424.203600-8-sashal@kernel.org>
Date: Sun, 28 Jan 2024 11:13:53 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Adrian Reber <areber@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	Andrei Vagin <avagin@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sasha Levin <sashal@...nel.org>,
	jirislaby@...nel.org,
	linux-serial@...r.kernel.org
Subject: [PATCH AUTOSEL 6.1 08/27] tty: allow TIOCSLCKTRMIOS with CAP_CHECKPOINT_RESTORE

From: Adrian Reber <areber@...hat.com>

[ Upstream commit e0f25b8992345aa5f113da2815f5add98738c611 ]

The capability CAP_CHECKPOINT_RESTORE was introduced to allow non-root
users to checkpoint and restore processes as non-root with CRIU.

This change extends CAP_CHECKPOINT_RESTORE to enable the CRIU option
'--shell-job' as non-root. CRIU's man-page describes the '--shell-job'
option like this:

  Allow one to dump shell jobs. This implies the restored task will
  inherit session and process group ID from the criu itself. This option
  also allows to migrate a single external tty connection, to migrate
  applications like top.

TIOCSLCKTRMIOS can only be done if the process has CAP_SYS_ADMIN and
this change extends it to CAP_SYS_ADMIN or CAP_CHECKPOINT_RESTORE.

With this change it is possible to checkpoint and restore processes
which have a tty connection as non-root if CAP_CHECKPOINT_RESTORE is
set.

Acked-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Adrian Reber <areber@...hat.com>
Acked-by: Andrei Vagin <avagin@...il.com>
Link: https://lore.kernel.org/r/20231208143656.1019-1-areber@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/tty/tty_ioctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index ad1cf51ecd11..41004720d4ae 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -859,7 +859,7 @@ int tty_mode_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
 			ret = -EFAULT;
 		return ret;
 	case TIOCSLCKTRMIOS:
-		if (!capable(CAP_SYS_ADMIN))
+		if (!checkpoint_restore_ns_capable(&init_user_ns))
 			return -EPERM;
 		copy_termios_locked(real_tty, &kterm);
 		if (user_termios_to_kernel_termios(&kterm,
@@ -876,7 +876,7 @@ int tty_mode_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
 			ret = -EFAULT;
 		return ret;
 	case TIOCSLCKTRMIOS:
-		if (!capable(CAP_SYS_ADMIN))
+		if (!checkpoint_restore_ns_capable(&init_user_ns))
 			return -EPERM;
 		copy_termios_locked(real_tty, &kterm);
 		if (user_termios_to_kernel_termios_1(&kterm,
-- 
2.43.0