selinux: format all invalid context as untrusted

The userspace tools expect all fields of the same name to be logged
consistently with the same encoding.  Since the invalid_context fields
contain untrusted strings in selinux_inode_setxattr()
and selinux_setprocattr(), encode all instances of this field the same
way as though they were untrusted even though
compute_sid_handle_invalid_context() and security_sid_mls_copy() are
trusted.

Please see github issue
https://github.com/linux-audit/audit-kernel/issues/57

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 20a089d0aca85339ff1d91db3468b5e03886f539..d3a8f6fbc552d95da09f280d0c1ee9186feddfa9 100644 (file)
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1584,6 +1584,7 @@ static int compute_sid_handle_invalid_context(
        struct policydb *policydb = &state->ss->policydb;
        char *s = NULL, *t = NULL, *n = NULL;
        u32 slen, tlen, nlen;
+       struct audit_buffer *ab;
 
        if (context_struct_to_string(policydb, scontext, &s, &slen))
                goto out;
@@ -1591,12 +1592,14 @@ static int compute_sid_handle_invalid_context(
                goto out;
        if (context_struct_to_string(policydb, newcontext, &n, &nlen))
                goto out;
-       audit_log(audit_context(), GFP_ATOMIC, AUDIT_SELINUX_ERR,
-                 "op=security_compute_sid invalid_context=%s"
-                 " scontext=%s"
-                 " tcontext=%s"
-                 " tclass=%s",
-                 n, s, t, sym_name(policydb, SYM_CLASSES, tclass-1));
+       ab = audit_log_start(audit_context(), GFP_ATOMIC, AUDIT_SELINUX_ERR);
+       audit_log_format(ab,
+                        "op=security_compute_sid invalid_context=");
+       /* no need to record the NUL with untrusted strings */
+       audit_log_n_untrustedstring(ab, n, nlen - 1);
+       audit_log_format(ab, " scontext=%s tcontext=%s tclass=%s",
+                        s, t, sym_name(policydb, SYM_CLASSES, tclass-1));
+       audit_log_end(ab);
 out:
        kfree(s);
        kfree(t);
@@ -3003,10 +3006,16 @@ int security_sid_mls_copy(struct selinux_state *state,
                if (rc) {
                        if (!context_struct_to_string(policydb, &newcon, &s,
                                                      &len)) {
-                               audit_log(audit_context(),
-                                         GFP_ATOMIC, AUDIT_SELINUX_ERR,
-                                         "op=security_sid_mls_copy "
-                                         "invalid_context=%s", s);
+                               struct audit_buffer *ab;
+
+                               ab = audit_log_start(audit_context(),
+                                                    GFP_ATOMIC,
+                                                    AUDIT_SELINUX_ERR);
+                               audit_log_format(ab,
+                                                "op=security_sid_mls_copy invalid_context=");
+                               /* don't record NUL with untrusted strings */
+                               audit_log_n_untrustedstring(ab, s, len - 1);
+                               audit_log_end(ab);
                                kfree(s);
                        }
                        goto out_unlock;