[PATCH] LSM: Add LSM syslog hook to 2.5.59

This patch adds the LSM security_syslog hook for controlling the
syslog(2) interface relative to 2.5.59 plus the previously posted
security_sysctl patch.  In response to earlier comments by Christoph,
the existing capability check for syslog(2) is moved into the
capability security module hook function, and a corresponding dummy
security module hook function is defined that provides traditional
superuser behavior.  The LSM hook is placed in do_syslog rather than
sys_syslog so that it is called when either the system call interface
or the /proc/kmsg interface is used.  SELinux uses this hook to
control access to the kernel message ring and to the console log
level.

include/linux/security.h

@@ -47,6 +47,7 @@ extern void cap_bprm_compute_creds (struct linux_binprm *bprm);
 extern int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid, int flags);
 extern void cap_task_kmod_set_label (void);
 extern void cap_task_reparent_to_init (struct task_struct *p);
+extern int cap_syslog (int type);
 
 /*
  * Values used in the task_security_ops calls
@@ -778,6 +779,12 @@ struct swap_info_struct;
  *	@tsk contains the task_struct for the process.
  *	@cap contains the capability <include/linux/capability.h>.
  *	Return 0 if the capability is granted for @tsk.
+ * @syslog:
+ *	Check permission before accessing the kernel message ring or changing
+ *	logging to the console.
+ *	See the syslog(2) manual page for an explanation of the @type values.  
+ *	@type contains the type of action.
+ *	Return 0 if permission is granted.
  *
  * @register_security:
  * 	allow module stacking.
@@ -808,6 +815,7 @@ struct security_operations {
 	int (*capable) (struct task_struct * tsk, int cap);
 	int (*quotactl) (int cmds, int type, int id, struct super_block * sb);
 	int (*quota_on) (struct file * f);
+	int (*syslog) (int type);
 
 	int (*bprm_alloc_security) (struct linux_binprm * bprm);
 	void (*bprm_free_security) (struct linux_binprm * bprm);
@@ -1013,6 +1021,11 @@ static inline int security_quota_on (struct file * file)
 	return security_ops->quota_on (file);
 }
 
+static inline int security_syslog(int type)
+{
+	return security_ops->syslog(type);
+}
+
 static inline int security_bprm_alloc (struct linux_binprm *bprm)
 {
 	return security_ops->bprm_alloc_security (bprm);
@@ -1627,6 +1640,11 @@ static inline int security_quota_on (struct file * file)
 	return 0;
 }
 
+static inline int security_syslog(int type)
+{
+	return cap_syslog(type);
+}
+
 static inline int security_bprm_alloc (struct linux_binprm *bprm)
 {
 	return 0;

kernel/printk.c

@@ -28,6 +28,7 @@
 #include <linux/config.h>
 #include <linux/delay.h>
 #include <linux/smp.h>
+#include <linux/security.h>
 
 #include <asm/uaccess.h>
 
@@ -161,6 +162,10 @@ int do_syslog(int type, char * buf, int len)
 	char c;
 	int error = 0;
 
+	error = security_syslog(type);
+	if (error)
+		return error;
+
 	switch (type) {
 	case 0:		/* Close log */
 		break;
@@ -273,8 +278,6 @@ int do_syslog(int type, char * buf, int len)
 
 asmlinkage long sys_syslog(int type, char * buf, int len)
 {
-	if ((type != 3) && !capable(CAP_SYS_ADMIN))
-		return -EPERM;
 	return do_syslog(type, buf, len);
 }
 

security/capability.c

@@ -262,6 +262,13 @@ void cap_task_reparent_to_init (struct task_struct *p)
 	return;
 }
 
+int cap_syslog (int type)
+{
+	if ((type != 3) && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	return 0;
+}
+
 EXPORT_SYMBOL(cap_capable);
 EXPORT_SYMBOL(cap_ptrace);
 EXPORT_SYMBOL(cap_capget);
@@ -272,6 +279,7 @@ EXPORT_SYMBOL(cap_bprm_compute_creds);
 EXPORT_SYMBOL(cap_task_post_setuid);
 EXPORT_SYMBOL(cap_task_kmod_set_label);
 EXPORT_SYMBOL(cap_task_reparent_to_init);
+EXPORT_SYMBOL(cap_syslog);
 
 #ifdef CONFIG_SECURITY
 
@@ -289,6 +297,8 @@ static struct security_operations capability_ops = {
 	.task_post_setuid =		cap_task_post_setuid,
 	.task_kmod_set_label =		cap_task_kmod_set_label,
 	.task_reparent_to_init =	cap_task_reparent_to_init,
+
+	.syslog =                       cap_syslog,
 };
 
 #if defined(CONFIG_SECURITY_CAPABILITIES_MODULE)

security/dummy.c

@@ -90,6 +90,13 @@ static int dummy_quota_on (struct file *f)
 	return 0;
 }
 
+static int dummy_syslog (int type)
+{
+	if ((type != 3) && current->euid)
+		return -EPERM;
+	return 0;
+}
+
 static int dummy_bprm_alloc_security (struct linux_binprm *bprm)
 {
 	return 0;
@@ -640,6 +647,7 @@ void security_fixup_ops (struct security_operations *ops)
 	set_to_dummy_if_null(ops, quotactl);
 	set_to_dummy_if_null(ops, quota_on);
 	set_to_dummy_if_null(ops, sysctl);
+	set_to_dummy_if_null(ops, syslog);
 	set_to_dummy_if_null(ops, bprm_alloc_security);
 	set_to_dummy_if_null(ops, bprm_free_security);
 	set_to_dummy_if_null(ops, bprm_compute_creds);