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>
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 @@
/**
* 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 440afe5e..971092c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -203,9 +203,9 @@
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 @@
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 @@
*
* 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;