<p><b>@smlng</b> requested changes on this pull request.</p>

<p>I read in the RFC and found something</p><hr>

<p>In <a href="https://github.com/RIOT-OS/RIOT/pull/11737#discussion_r298571034">sys/net/gnrc/application_layer/tftp/gnrc_tftp.c</a>:</p>
<pre style='color:#555'>> @@ -1047,6 +1047,10 @@ int _tftp_decode_start(tftp_context_t *ctxt, uint8_t *buf, gnrc_pktsnip_t *outbu
 
     /* decode the TFTP transfer mode */
     for (uint32_t idx = 0; idx < ARRAY_LEN(_tftp_modes); ++idx) {
+        if (_tftp_modes[idx].len > (inpkt->size - sizeof(*hdr) - fnlen)) {
</pre>
<p>according to the header format in <a href="https://tools.ietf.org/html/rfc1350#appendix-I" rel="nofollow">RFC</a> all strings are 0 terminated so this can be simplified to (and also be more readable):</p>
<pre><code>if (_tftp_modes[idx].len > strlen(str_mode) {
</code></pre>
<p>do you agree?</p>

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