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>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/include/linux/security.h b/include/linux/security.h
index 26eca85b2417..a4dc74d86ac6 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;
@@ -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)