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SubjectRe: [PATCH 1/2] syslog: distinguish between /proc/kmsg and syscalls
Quoting Kees Cook (kees.cook@canonical.com):
> 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>

Acked-by: Serge Hallyn <serue@us.ibm.com>

However, I know James said 'you can just pass in 0 or 1', but
I think the callers will be much clearer if you

#define SYSLOG_FROM_CALL 0
#define SYSLOG_FROM_FILE 1

or something shorter if you can think of it

> ---
> 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@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
> +
> +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 */

Egads this comment confused me for a minute - can you change
that to something like 'requires CAP_SYS_ADMIN'? I then misread
the '!=' to be == and thought you were inverting your logic.

> + 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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