linux-kernel - [PATCH ghak57 V1] selinux: format all invalid context as untrusted

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Date:   Thu, 13 Jun 2019 14:43:21 -0400
From:   Richard Guy Briggs <rgb@...hat.com>
To:     Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        SElinux list <selinux@...r.kernel.org>
Cc:     Paul Moore <paul@...l-moore.com>,
        Ondrej Mosnacec <omosnace@...hat.com>,
        Eric Paris <eparis@...hat.com>,
        Steve Grubb <sgrubb@...hat.com>,
        Richard Guy Briggs <rgb@...hat.com>
Subject: [PATCH ghak57 V1] selinux: format all invalid context as untrusted

All instances of one field type should be encoded in the same way.
Since some invalid_context fields can contain untrusted strings, encode
all instances of this field the same way.

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

Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
---
Passes audit-testsuite.

 security/selinux/ss/services.c | 48 +++++++++++++++++++++++++++++++++---------
 1 file changed, 38 insertions(+), 10 deletions(-)

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index cc043bc8fd4c..817576802f7d 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1588,6 +1588,8 @@ 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;
+	size_t audit_size;
 
 	if (context_struct_to_string(policydb, scontext, &s, &slen))
 		goto out;
@@ -1595,12 +1597,22 @@ 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));
+	/* We strip a nul only if it is at the end, otherwise the
+	 * context contains a nul and we should audit that */
+	if (n) {
+		if (n[nlen - 1] == '\0')
+			audit_size = nlen - 1;
+		else
+			audit_size = nlen;
+	} else {
+		audit_size = 0;
+	}
+	ab = audit_log_start(audit_context(), GFP_ATOMIC, AUDIT_SELINUX_ERR);
+	audit_log_format(ab, "op=security_compute_sid invalid_context=");
+	audit_log_n_untrustedstring(ab, n, audit_size);
+	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);
@@ -3007,10 +3019,26 @@ 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;
+				size_t audit_size;
+
+				/* We strip a nul only if it is at the
+				 * end, otherwise the context contains a
+				 * nul and we should audit that */
+				if (s) {
+					if (s[len - 1] == '\0')
+						audit_size = len - 1;
+					else
+						audit_size = len;
+				} else {
+					audit_size = 0;
+				}
+				ab = audit_log_start(audit_context(),
+						     GFP_ATOMIC,
+						     AUDIT_SELINUX_ERR);
+				audit_log_format(ab, "op=security_sid_mls_copy invalid_context=");
+				audit_log_n_untrustedstring(ab, s, audit_size);
+				audit_log_end(ab);
 				kfree(s);
 			}
 			goto out_unlock;
-- 
1.8.3.1