Message-ID: <20100203191542.GE19355@outflux.net>
Date:	Wed, 3 Feb 2010 11:15:42 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	James Morris <jmorris@...ei.org>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	linux-security-module@...r.kernel.org,
	Eric Paris <eparis@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Simon Kagstrom <simon.kagstrom@...insight.net>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Robin Getz <rgetz@...log.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Paul Moore <paul.moore@...com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Etienne Basset <etienne.basset@...ericable.fr>,
	"David P. Quigley" <dpquigl@...ho.nsa.gov>,
	LKLM <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] syslog: distinguish between /proc/kmsg and syscalls

This allows the LSM to distinguish between syslog functions originating
from /proc/kmsg access and direct syscalls.  By default, the commoncaps
will now no longer require CAP_SYS_ADMIN to read an opened /proc/kmsg
file descriptor.  For example the kernel syslog reader can now drop
privileges after opening /proc/kmsg, instead of staying privileged with
CAP_SYS_ADMIN.  MAC systems that implement security_syslog have unchanged
behavior.

Signed-off-by: Kees Cook <kees.cook@...onical.com>
---
 fs/proc/kmsg.c             |   13 ++++++-------
 include/linux/security.h   |   11 ++++++-----
 include/linux/syslog.h     |   26 ++++++++++++++++++++++++++
 kernel/printk.c            |    7 ++++---
 security/commoncap.c       |    7 ++++++-
 security/security.c        |    4 ++--
 security/selinux/hooks.c   |    5 +++--
 security/smack/smack_lsm.c |    4 ++--
 8 files changed, 55 insertions(+), 22 deletions(-)
 create mode 100644 include/linux/syslog.h

diff --git a/fs/proc/kmsg.c b/fs/proc/kmsg.c
index 7ca7834..4a08999 100644
--- a/fs/proc/kmsg.c
+++ b/fs/proc/kmsg.c
@@ -12,37 +12,36 @@
 #include <linux/poll.h>
 #include <linux/proc_fs.h>
 #include <linux/fs.h>
+#include <linux/syslog.h>
 
 #include <asm/uaccess.h>
 #include <asm/io.h>
 
 extern wait_queue_head_t log_wait;
 
-extern int do_syslog(int type, char __user *bug, int count);
-
 static int kmsg_open(struct inode * inode, struct file * file)
 {
-	return do_syslog(1,NULL,0);
+	return do_syslog(1, NULL, 0, 1);
 }
 
 static int kmsg_release(struct inode * inode, struct file * file)
 {
-	(void) do_syslog(0,NULL,0);
+	(void) do_syslog(0, NULL, 0, 1);
 	return 0;
 }
 
 static ssize_t kmsg_read(struct file *file, char __user *buf,
 			 size_t count, loff_t *ppos)
 {
-	if ((file->f_flags & O_NONBLOCK) && !do_syslog(9, NULL, 0))
+	if ((file->f_flags & O_NONBLOCK) && !do_syslog(9, NULL, 0, 1))
 		return -EAGAIN;
-	return do_syslog(2, buf, count);
+	return do_syslog(2, buf, count, 1);
 }
 
 static unsigned int kmsg_poll(struct file *file, poll_table *wait)
 {
 	poll_wait(file, &log_wait, wait);
-	if (do_syslog(9, NULL, 0))
+	if (do_syslog(9, NULL, 0, 1))
 		return POLLIN | POLLRDNORM;
 	return 0;
 }
diff --git a/include/linux/security.h b/include/linux/security.h
index 2c627d3..10955c3 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -76,7 +76,7 @@ extern int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 extern int cap_task_setscheduler(struct task_struct *p, int policy, struct sched_param *lp);
 extern int cap_task_setioprio(struct task_struct *p, int ioprio);
 extern int cap_task_setnice(struct task_struct *p, int nice);
-extern int cap_syslog(int type);
+extern int cap_syslog(int type, int from_file);
 extern int cap_vm_enough_memory(struct mm_struct *mm, long pages);
 
 struct msghdr;
@@ -1348,6 +1348,7 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  *	logging to the console.
  *	See the syslog(2) manual page for an explanation of the @type values.
  *	@type contains the type of action.
+ *	@from_file indicates the context of action (if it came from /proc).
  *	Return 0 if permission is granted.
  * @settime:
  *	Check permission to change the system time.
@@ -1462,7 +1463,7 @@ struct security_operations {
 	int (*sysctl) (struct ctl_table *table, int op);
 	int (*quotactl) (int cmds, int type, int id, struct super_block *sb);
 	int (*quota_on) (struct dentry *dentry);
-	int (*syslog) (int type);
+	int (*syslog) (int type, int from_file);
 	int (*settime) (struct timespec *ts, struct timezone *tz);
 	int (*vm_enough_memory) (struct mm_struct *mm, long pages);
 
@@ -1761,7 +1762,7 @@ int security_acct(struct file *file);
 int security_sysctl(struct ctl_table *table, int op);
 int security_quotactl(int cmds, int type, int id, struct super_block *sb);
 int security_quota_on(struct dentry *dentry);
-int security_syslog(int type);
+int security_syslog(int type, int from_file);
 int security_settime(struct timespec *ts, struct timezone *tz);
 int security_vm_enough_memory(long pages);
 int security_vm_enough_memory_mm(struct mm_struct *mm, long pages);
@@ -2007,9 +2008,9 @@ static inline int security_quota_on(struct dentry *dentry)
 	return 0;
 }
 
-static inline int security_syslog(int type)
+static inline int security_syslog(int type, int from_file)
 {
-	return cap_syslog(type);
+	return cap_syslog(type, from_file);
 }
 
 static inline int security_settime(struct timespec *ts, struct timezone *tz)
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
new file mode 100644
index 0000000..f8c9d94
--- /dev/null
+++ b/include/linux/syslog.h
@@ -0,0 +1,26 @@
+/*  Syslog internals
+ *
+ *  Copyright 2010 Canonical, Ltd.
+ *  Author: Kees Cook <kees.cook@...onical.com>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2, or (at your option)
+ *  any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; see the file COPYING.  If not, write to
+ *  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef _LINUX_SYSLOG_H
+#define _LINUX_SYSLOG_H
+
+int do_syslog(int type, char __user *buf, int count, int from_file);
+
+#endif /* _LINUX_SYSLOG_H */
diff --git a/kernel/printk.c b/kernel/printk.c
index 1751c45..4bc1412 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -35,6 +35,7 @@
 #include <linux/kexec.h>
 #include <linux/ratelimit.h>
 #include <linux/kmsg_dump.h>
+#include <linux/syslog.h>
 
 #include <asm/uaccess.h>
 
@@ -273,14 +274,14 @@ static inline void boot_delay_msec(void)
  *	9 -- Return number of unread characters in the log buffer
  *     10 -- Return size of the log buffer
  */
-int do_syslog(int type, char __user *buf, int len)
+int do_syslog(int type, char __user *buf, int len, int from_file)
 {
 	unsigned i, j, limit, count;
 	int do_clear = 0;
 	char c;
 	int error = 0;
 
-	error = security_syslog(type);
+	error = security_syslog(type, from_file);
 	if (error)
 		return error;
 
@@ -417,7 +418,7 @@ out:
 
 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 {
-	return do_syslog(type, buf, len);
+	return do_syslog(type, buf, len, 0);
 }
 
 /*
diff --git a/security/commoncap.c b/security/commoncap.c
index f800fdb..aaf123f 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -27,6 +27,7 @@
 #include <linux/sched.h>
 #include <linux/prctl.h>
 #include <linux/securebits.h>
+#include <linux/syslog.h>
 
 /*
  * If a non-root user executes a setuid-root binary in
@@ -888,12 +889,16 @@ error:
 /**
  * cap_syslog - Determine whether syslog function is permitted
  * @type: Function requested
+ * @from_file: Whether this request came from an open file (i.e. /proc)
  *
  * Determine whether the current process is permitted to use a particular
  * syslog function, returning 0 if permission is granted, -ve if not.
  */
-int cap_syslog(int type)
+int cap_syslog(int type, int from_file)
 {
+	/* /proc/kmsg can open be opened by CAP_SYS_ADMIN */
+	if (type != 1 && from_file)
+		return 0;
 	if ((type != 3 && type != 10) && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
 	return 0;
diff --git a/security/security.c b/security/security.c
index 24e060b..568b1bd 100644
--- a/security/security.c
+++ b/security/security.c
@@ -203,9 +203,9 @@ int security_quota_on(struct dentry *dentry)
 	return security_ops->quota_on(dentry);
 }
 
-int security_syslog(int type)
+int security_syslog(int type, int from_file)
 {
-	return security_ops->syslog(type);
+	return security_ops->syslog(type, from_file);
 }
 
 int security_settime(struct timespec *ts, struct timezone *tz)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9a2ee84..744785c 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -76,6 +76,7 @@
 #include <linux/selinux.h>
 #include <linux/mutex.h>
 #include <linux/posix-timers.h>
+#include <linux/syslog.h>
 
 #include "avc.h"
 #include "objsec.h"
@@ -2049,11 +2050,11 @@ static int selinux_quota_on(struct dentry *dentry)
 	return dentry_has_perm(cred, NULL, dentry, FILE__QUOTAON);
 }
 
-static int selinux_syslog(int type)
+static int selinux_syslog(int type, int from_file)
 {
 	int rc;
 
-	rc = cap_syslog(type);
+	rc = cap_syslog(type, from_file);
 	if (rc)
 		return rc;
 
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 529c9ca..b271e18 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -157,12 +157,12 @@ static int smack_ptrace_traceme(struct task_struct *ptp)
  *
  * Returns 0 on success, error code otherwise.
  */
-static int smack_syslog(int type)
+static int smack_syslog(int type, int from_file)
 {
 	int rc;
 	char *sp = current_security();
 
-	rc = cap_syslog(type);
+	rc = cap_syslog(type, from_file);
 	if (rc != 0)
 		return rc;
 
-- 
1.6.5


-- 
Kees Cook
Ubuntu Security Team
--
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