Avoid double free when processing DTLS packets.

The |item| variable, in both of these cases, may contain a pointer to a
|pitem| structure within |s->d1->buffered_messages|. It was being freed
in the error case while still being in |buffered_messages|. When the
error later caused the |SSL*| to be destroyed, the item would be double
freed.

Thanks to Wah-Teh Chang for spotting that the fix in 1632ef74 was
inconsistent with the other error paths (but correct).

Fixes CVE-2014-3505

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Emilia Käsper <emilia@openssl.org>

(Imported from upstream's 49850075555893c9c60d5b981deb697f3b9515ea)

Change-Id: Ie40007184f6194ba032b4213c18d36254e80aaa6
Reviewed-on: https://boringssl-review.googlesource.com/1432
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

ssl/d1_both.c

@@ -701,8 +701,7 @@ dtls1_reassemble_fragment(SSL *s, struct hm_header_st* msg_hdr, int *ok)
 	return DTLS1_HM_FRAGMENT_RETRY;
 
 err:
-	if (frag != NULL) dtls1_hm_fragment_free(frag);
-	if (item != NULL) OPENSSL_free(item);
+	if (frag != NULL && item == NULL) dtls1_hm_fragment_free(frag);
 	*ok = 0;
 	return i;
 	}
@@ -786,8 +785,7 @@ dtls1_process_out_of_seq_message(SSL *s, struct hm_header_st* msg_hdr, int *ok)
 	return DTLS1_HM_FRAGMENT_RETRY;
 
 err:
-	if ( frag != NULL) dtls1_hm_fragment_free(frag);
-	if ( item != NULL) OPENSSL_free(item);
+	if (frag != NULL && item == NULL) dtls1_hm_fragment_free(frag);
 	*ok = 0;
 	return i;
 	}