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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
    > --
    > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at http://vger.kernel.org/majordomo-info.html


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