Commit 00234592 authored by Kees Cook's avatar Kees Cook Committed by James Morris
Browse files

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
Signed-off-by: default avatarKees Cook <>
Acked-by: default avatarSerge Hallyn <>
Acked-by: default avatarJohn Johansen <>
Signed-off-by: default avatarJames Morris <>
parent 0719aaf5
......@@ -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_FROM_FILE);
static int kmsg_release(struct inode * inode, struct file * file)
(void) do_syslog(0,NULL,0);
(void) do_syslog(0, NULL, 0, SYSLOG_FROM_FILE);
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_FROM_FILE))
return -EAGAIN;
return do_syslog(2, buf, count);
return do_syslog(2, buf, count, SYSLOG_FROM_FILE);
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_FROM_FILE))
return 0;
......@@ -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, bool from_file);
extern int cap_vm_enough_memory(struct mm_struct *mm, long pages);
struct msghdr;
......@@ -1349,6 +1349,7 @@ 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.
......@@ -1463,7 +1464,7 @@ 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, bool from_file);
int (*settime) (struct timespec *ts, struct timezone *tz);
int (*vm_enough_memory) (struct mm_struct *mm, long pages);
......@@ -1762,7 +1763,7 @@ 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, bool 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);
......@@ -2008,9 +2009,9 @@ 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, bool from_file)
return cap_syslog(type);
return cap_syslog(type, from_file);
static inline int security_settime(struct timespec *ts, struct timezone *tz)
/* Syslog internals
* Copyright 2010 Canonical, Ltd.
* Author: Kees Cook <>
* 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
* 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.
int do_syslog(int type, char __user *buf, int count, bool from_file);
#endif /* _LINUX_SYSLOG_H */
......@@ -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, bool 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, SYSLOG_FROM_CALL);
......@@ -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, bool 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;
......@@ -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, bool from_file)
return security_ops->syslog(type);
return security_ops->syslog(type, from_file);
int security_settime(struct timespec *ts, struct timezone *tz)
......@@ -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, bool from_file)
int rc;
rc = cap_syslog(type);
rc = cap_syslog(type, from_file);
if (rc)
return rc;
......@@ -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, bool from_file)
int rc;
char *sp = current_security();
rc = cap_syslog(type);
rc = cap_syslog(type, from_file);
if (rc != 0)
return rc;
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