Re: [PATCH v2 1/2] syslog: distinguish between /proc/kmsg and syscalls

[John Johansen]

Serge E. Hallyn wrote:
> Quoting Kees Cook (kees.cook@xxxxxxxxxxxxx):
>> 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@xxxxxxxxxxxxx>
> 
> Acked-by: Serge Hallyn <serue@xxxxxxxxxx>
Acked-by: John Johansen <john.johansen@xxxxxxxxxxxxx>

> 
>> ---
>>  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   |    5 +++--
>>  security/smack/smack_lsm.c |    4 ++--
>>  8 files changed, 59 insertions(+), 22 deletions(-)
>>  create mode 100644 include/linux/syslog.h
>>
>> diff --git a/fs/proc/kmsg.c b/fs/proc/kmsg.c
>> index 7ca7834..6a3d843 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_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 POLLIN | POLLRDNORM;
>>  	return 0;
>>  }
>> diff --git a/include/linux/security.h b/include/linux/security.h
>> index 2c627d3..106786e 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, bool 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, bool 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, 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);
>> @@ -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, bool 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..5f02b18
>> --- /dev/null
>> +++ b/include/linux/syslog.h
>> @@ -0,0 +1,29 @@
>> +/*  Syslog internals
>> + *
>> + *  Copyright 2010 Canonical, Ltd.
>> + *  Author: Kees Cook <kees.cook@xxxxxxxxxxxxx>
>> + *
>> + *  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_FROM_CALL 0
>> +#define SYSLOG_FROM_FILE 1
>> +
>> +int do_syslog(int type, char __user *buf, int count, bool from_file);
>> +
>> +#endif /* _LINUX_SYSLOG_H */
>> diff --git a/kernel/printk.c b/kernel/printk.c
>> index 1751c45..1771b34 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, 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);
>>  }
>>
>>  /*
>> diff --git a/security/commoncap.c b/security/commoncap.c
>> index f800fdb..677fad9 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, 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;
>> diff --git a/security/security.c b/security/security.c
>> index 24e060b..9a127ae 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, bool 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..a4862a0 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, bool 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..a5721b3 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, bool 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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