linux-kernel - [PATCH 5.1 017/115] selinux: log raw contexts as untrusted strings

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Date:   Mon, 17 Jun 2019 23:08:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ondrej Mosnacek <omosnace@...hat.com>,
        Richard Guy Briggs <rgb@...hat.com>,
        Paul Moore <paul@...l-moore.com>
Subject: [PATCH 5.1 017/115] selinux: log raw contexts as untrusted strings

From: Ondrej Mosnacek <omosnace@...hat.com>

commit aff7ed4851680d0d28ad9f52cd2f99213e1371b2 upstream.

These strings may come from untrusted sources (e.g. file xattrs) so they
need to be properly escaped.

Reproducer:
    # setenforce 0
    # touch /tmp/test
    # setfattr -n security.selinux -v 'kuřecí řízek' /tmp/test
    # runcon system_u:system_r:sshd_t:s0 cat /tmp/test
    (look at the generated AVCs)

Actual result:
    type=AVC [...] trawcon=kuřecí řízek

Expected result:
    type=AVC [...] trawcon=6B75C5996563C3AD20C599C3AD7A656B

Fixes: fede148324c3 ("selinux: log invalid contexts in AVCs")
Cc: stable@...r.kernel.org # v5.1+
Signed-off-by: Ondrej Mosnacek <omosnace@...hat.com>
Acked-by: Richard Guy Briggs <rgb@...hat.com>
Signed-off-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 security/selinux/avc.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -739,14 +739,20 @@ static void avc_audit_post_callback(stru
 	rc = security_sid_to_context_inval(sad->state, sad->ssid, &scontext,
 					   &scontext_len);
 	if (!rc && scontext) {
-		audit_log_format(ab, " srawcon=%s", scontext);
+		if (scontext_len && scontext[scontext_len - 1] == '\0')
+			scontext_len--;
+		audit_log_format(ab, " srawcon=");
+		audit_log_n_untrustedstring(ab, scontext, scontext_len);
 		kfree(scontext);
 	}
 
 	rc = security_sid_to_context_inval(sad->state, sad->tsid, &scontext,
 					   &scontext_len);
 	if (!rc && scontext) {
-		audit_log_format(ab, " trawcon=%s", scontext);
+		if (scontext_len && scontext[scontext_len - 1] == '\0')
+			scontext_len--;
+		audit_log_format(ab, " trawcon=");
+		audit_log_n_untrustedstring(ab, scontext, scontext_len);
 		kfree(scontext);
 	}
 }