selinux: log raw contexts as untrusted strings

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@vger.kernel.org # v5.1+
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 8346a4f..a99be50 100644 (file)
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -739,14 +739,20 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
        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);
        }
 }