From ce10d1b72b4da3c98bbbcb1b945687d964c31923 Mon Sep 17 00:00:00 2001

From: Josh Boyer <jwboyer@redhat.com>

Date: Tue, 9 Apr 2013 11:08:13 -0400

Subject: [PATCH] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg

The dmesg_restrict sysctl currently covers the syslog method for access

dmesg, however /dev/kmsg isn't covered by the same protections.  Most

people haven't noticed because util-linux dmesg(1) defaults to using the

syslog method for access in older versions.  With util-linux dmesg(1)

defaults to reading directly from /dev/kmsg.

Fix this by reworking all of the access methods to use the

check_syslog_permissions function and adding checks to devkmsg_open and

devkmsg_read.

This fixes https://bugzilla.redhat.com/show_bug.cgi?id=903192

Reported-by: Christian Kujau <lists@nerdbynature.de>

CC: stable@vger.kernel.org

Signed-off-by: Eric Paris <eparis@redhat.com>

Signed-off-by: Josh Boyer <jwboyer@redhat.com>

---

 kernel/printk.c | 91 +++++++++++++++++++++++++++++----------------------------

 1 file changed, 47 insertions(+), 44 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c

index abbdd9e..5541095 100644

--- a/kernel/printk.c

+++ b/kernel/printk.c

@@ -368,6 +368,46 @@ static void log_store(int facility, int level,

 	log_next_seq++;

 }

+#ifdef CONFIG_SECURITY_DMESG_RESTRICT

+int dmesg_restrict = 1;

+#else

+int dmesg_restrict;

+#endif

+

+static int syslog_action_restricted(int type)

+{

+	if (dmesg_restrict)

+		return 1;

+	/* Unless restricted, we allow "read all" and "get buffer size" for everybody */

+	return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;

+}

+

+static int check_syslog_permissions(int type, bool from_file)

+{

+	/*

+	 * If this is from /proc/kmsg and we've already opened it, then we've

+	 * already done the capabilities checks at open time.

+	 */

+	if (from_file && type != SYSLOG_ACTION_OPEN)

+		goto ok;

+

+	if (syslog_action_restricted(type)) {

+		if (capable(CAP_SYSLOG))

+			goto ok;

+		/* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */

+		if (capable(CAP_SYS_ADMIN)) {

+			printk_once(KERN_WARNING "%s (%d): "

+				 "Attempt to access syslog with CAP_SYS_ADMIN "

+				 "but no CAP_SYSLOG (deprecated).\n",

+				 current->comm, task_pid_nr(current));

+			goto ok;

+		}

+		return -EPERM;

+	}

+ok:

+	return security_syslog(type);

+}

+

 /* /dev/kmsg - userspace message inject/listen interface */

 struct devkmsg_user {

 	u64 seq;

@@ -443,10 +483,16 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,

 	char cont = '-';

 	size_t len;

 	ssize_t ret;

+	int err;

 	if (!user)

 		return -EBADF;

+	err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,

+		SYSLOG_FROM_FILE);

+	if (err)

+		return err;

+

 	ret = mutex_lock_interruptible(&user->lock);

 	if (ret)

 		return ret;

@@ -624,7 +670,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)

 	if ((file->f_flags & O_ACCMODE) == O_WRONLY)

 		return 0;

-	err = security_syslog(SYSLOG_ACTION_READ_ALL);

+	err = check_syslog_permissions(SYSLOG_ACTION_OPEN, SYSLOG_FROM_FILE);

 	if (err)

 		return err;

@@ -817,45 +863,6 @@ static inline void boot_delay_msec(int level)

 }

 #endif

-#ifdef CONFIG_SECURITY_DMESG_RESTRICT

-int dmesg_restrict = 1;

-#else

-int dmesg_restrict;

-#endif

-

-static int syslog_action_restricted(int type)

-{

-	if (dmesg_restrict)

-		return 1;

-	/* Unless restricted, we allow "read all" and "get buffer size" for everybody */

-	return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;

-}

-

-static int check_syslog_permissions(int type, bool from_file)

-{

-	/*

-	 * If this is from /proc/kmsg and we've already opened it, then we've

-	 * already done the capabilities checks at open time.

-	 */

-	if (from_file && type != SYSLOG_ACTION_OPEN)

-		return 0;

-

-	if (syslog_action_restricted(type)) {

-		if (capable(CAP_SYSLOG))

-			return 0;

-		/* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */

-		if (capable(CAP_SYS_ADMIN)) {

-			printk_once(KERN_WARNING "%s (%d): "

-				 "Attempt to access syslog with CAP_SYS_ADMIN "

-				 "but no CAP_SYSLOG (deprecated).\n",

-				 current->comm, task_pid_nr(current));

-			return 0;

-		}

-		return -EPERM;

-	}

-	return 0;

-}

-

 #if defined(CONFIG_PRINTK_TIME)

 static bool printk_time = 1;

 #else

@@ -1131,10 +1138,6 @@ 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;

-- 

1.8.1.4