[PATCH v2 2/2] tftp: ignore trailing garbage in the request

[Denys Vlasenko]

On Mon, Sep 1, 2014 at 10:24 PM, Aaro Koskinen <aaro.koskinen at iki.fi> wrote:
> The firmware in some HP PA-RISC boxes is always sending fixed
> 512-byte requests, and sometimes there is some garbage at the end
> which makes busybox to reject the request. Ignore any characters after
> the last NUL.

How about this?

        result = recv_from_to(STDIN_FILENO,
                        G.block_buf, sizeof(G.block_buf) + 1,
                        /* ^^^ sizeof+1 to reliably detect oversized input */
                        0 /* flags */,
                        &peer_lsa->u.sa, &our_lsa->u.sa, our_lsa->len);

        error_msg = "malformed packet";
        opcode = ntohs(*(uint16_t*)G.block_buf);
        if (result < 4 || result > sizeof(G.block_buf)
        /*|| G.block_buf[result-1] != '\0' - bug compatibility, see below */
         || (IF_FEATURE_TFTP_PUT(opcode != TFTP_RRQ) /* not download */
             IF_GETPUT(&&)
             IF_FEATURE_TFTP_GET(opcode != TFTP_WRQ) /* not upload */
            )
        ) {
                goto err;
        }
        /* Some HP PA-RISC firmware always sends fixed 512-byte requests,
         * with trailing garbage.
         * Support that by not requiring NUL to be the last byte (see above).
         * To make strXYZ() ops safe, force NUL termination:
         */
        G.block_buf_tail[0] = '\0';