linux-kernel - [PATCH 3.16.y-ckt 177/185] security_syslog() should be called once only

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Message-Id: <1436951580-15977-178-git-send-email-luis.henriques@canonical.com>
Date:	Wed, 15 Jul 2015 10:12:52 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Vasily Averin <vvs@...tuozzo.com>,
	Kees Cook <keescook@...omium.org>,
	Josh Boyer <jwboyer@...hat.com>,
	Eric Paris <eparis@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 177/185] security_syslog() should be called once only

3.16.7-ckt15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vasily Averin <vvs@...tuozzo.com>

commit d194e5d666225b04c7754471df0948f645b6ab3a upstream.

The final version of commit 637241a900cb ("kmsg: honor dmesg_restrict
sysctl on /dev/kmsg") lost few hooks, as result security_syslog() are
processed incorrectly:

- open of /dev/kmsg checks syslog access permissions by using
  check_syslog_permissions() where security_syslog() is not called if
  dmesg_restrict is set.

- syslog syscall and /proc/kmsg calls do_syslog() where security_syslog
  can be executed twice (inside check_syslog_permissions() and then
  directly in do_syslog())

With this patch security_syslog() is called once only in all
syslog-related operations regardless of dmesg_restrict value.

Fixes: 637241a900cb ("kmsg: honor dmesg_restrict sysctl on /dev/kmsg")
Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Josh Boyer <jwboyer@...hat.com>
Cc: Eric Paris <eparis@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 kernel/printk/printk.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index cce20d2f38d5..f7f6f7e5ff8a 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -478,11 +478,11 @@ static int check_syslog_permissions(int type, bool from_file)
 	 * already done the capabilities checks at open time.
 	 */
 	if (from_file && type != SYSLOG_ACTION_OPEN)
-		return 0;
+		goto ok;
 
 	if (syslog_action_restricted(type)) {
 		if (capable(CAP_SYSLOG))
-			return 0;
+			goto ok;
 		/*
 		 * For historical reasons, accept CAP_SYS_ADMIN too, with
 		 * a warning.
@@ -492,10 +492,11 @@ static int check_syslog_permissions(int type, bool from_file)
 				     "CAP_SYS_ADMIN but no CAP_SYSLOG "
 				     "(deprecated).\n",
 				 current->comm, task_pid_nr(current));
-			return 0;
+			goto ok;
 		}
 		return -EPERM;
 	}
+ok:
 	return security_syslog(type);
 }
 
@@ -1221,10 +1222,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
 	if (error)
 		goto out;
 
-	error = security_syslog(type);
-	if (error)
-		return error;
-
 	switch (type) {
 	case SYSLOG_ACTION_CLOSE:	/* Close log */
 		break;
--
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