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Subject[PATCH] 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@canonical.com>
---
fs/proc/kmsg.c | 14 +++++++-------
include/linux/security.h | 11 ++++++-----
include/linux/syslog.h | 29 +++++++++++++++++++++++++++++
kernel/printk.c | 7 ++++---
security/commoncap.c | 7 ++++++-
security/security.c | 4 ++--
security/selinux/hooks.c | 4 ++--
security/smack/smack_lsm.c | 4 ++--
8 files changed, 58 insertions(+), 22 deletions(-)
create mode 100644 include/linux/syslog.h
diff --git a/fs/proc/kmsg.c b/fs/proc/kmsg.c
index 7ca7834..4f52b68 100644
--- a/fs/proc/kmsg.c
+++ b/fs/proc/kmsg.c
@@ -12,37 +12,37 @@
#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, SYSLOG_CONTEXT_PROC);
}

static int kmsg_release(struct inode * inode, struct file * file)
{
- (void) do_syslog(0,NULL,0);
+ (void) do_syslog(0, NULL, 0, SYSLOG_CONTEXT_PROC);
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, SYSLOG_CONTEXT_PROC))
return -EAGAIN;
- return do_syslog(2, buf, count);
+ return do_syslog(2, buf, count, SYSLOG_CONTEXT_PROC);
}

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, SYSLOG_CONTEXT_PROC))
return POLLIN | POLLRDNORM;
return 0;
}
diff --git a/include/linux/security.h b/include/linux/security.h
index 2c627d3..174f834 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 context);
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.
+ * @context contains the context of action (/proc or syscall).
* 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 context);
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 context);
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 context)
{
- return cap_syslog(type);
+ return cap_syslog(type, context);
}

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..563c2a9
--- /dev/null
+++ b/include/linux/syslog.h
@@ -0,0 +1,29 @@
+/* Syslog internals
+ *
+ * Copyright 2010 Canonical, Ltd.
+ * Author: Kees Cook <kees.cook@canonical.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
+
+#define SYSLOG_CONTEXT_SYSCALL 0
+#define SYSLOG_CONTEXT_PROC 1
+
+int do_syslog(int type, char __user *buf, int count, int context);
+
+#endif /* _LINUX_SYSLOG_H */
diff --git a/kernel/printk.c b/kernel/printk.c
index 1751c45..a131ad6 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 context)
{
unsigned i, j, limit, count;
int do_clear = 0;
char c;
int error = 0;

- error = security_syslog(type);
+ error = security_syslog(type, context);
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, SYSLOG_CONTEXT_SYSCALL);
}

/*
diff --git a/security/commoncap.c b/security/commoncap.c
index f800fdb..9c965dc 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
+ * @context: What context this request came from (/proc or syscall)
*
* 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 context)
{
+ /* /proc/kmsg can open be opened by CAP_SYS_ADMIN */
+ if (type != 1 && context == SYSLOG_CONTEXT_PROC)
+ 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..38a8994 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 context)
{
- return security_ops->syslog(type);
+ return security_ops->syslog(type, context);
}

int security_settime(struct timespec *ts, struct timezone *tz)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9a2ee84..f476afa 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2049,11 +2049,11 @@ 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 context)
{
int rc;

- rc = cap_syslog(type);
+ rc = cap_syslog(type, context);
if (rc)
return rc;

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 529c9ca..a56ab5c 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 context)
{
int rc;
char *sp = current_security();

- rc = cap_syslog(type);
+ rc = cap_syslog(type, context);
if (rc != 0)
return rc;

--
1.6.5
--
Kees Cook
Ubuntu Security Team


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