linux-kernel - [PATCH v2] security_syslog() should be called once only

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Date:	Sun, 24 May 2015 19:18:40 +0300
From:	Vasily Averin <vvs@...tuozzo.com>
To:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Kees Cook <keescook@...omium.org>, Josh Boyer <jwboyer@...hat.com>,
	Eric Paris <eparis@...hat.com>
Subject: [PATCH v2] security_syslog() should be called once only

v2: subject changed, patch comment modified

Fixes: 637241a900cb ("kmsg: honor dmesg_restrict sysctl on /dev/kmsg")

Final version of patch 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.

Signed-off-by: Vasily Averin <vvs@...tuozzo.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 c099b08..bff0169 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -484,11 +484,11 @@ 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.
@@ -498,10 +498,11 @@ 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);
 }
 
@@ -1263,10 +1264,6 @@ 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;
-- 
1.9.1

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