[Bug 6146] pxe/tftp sends pxelinux.0 to client with corrupted file name - client can't dowload file.

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=6146

--- Comment #3 from Jeff Pohlmeyer <yetanothergeek at gmail.com> ---
I have encountered this problem as well. I can send more information if needed,
but it looks like the difference is that dnsmasq adds a terminating NULL byte
to the end of the filename, but udhcpd does not.

If I understand the RFC correctly, busybox is actually doing the right thing,
but some PXE clients do not.

According to RFC 2132:

"Options containing NVT ASCII data SHOULD NOT include a trailing NULL; however,
the receiver of such options MUST be prepared to delete trailing nulls if they
exist.  The receiver MUST NOT require that a trailing null be included in the
data."

But from a practical standpoint, including the NULL byte violates the RFC but
satisfies some broken clients. On the other hand, if a client is in compliance
with the RFC, the extra NULL terminator should not be a problem.

This happens with the pre-packaged Arch Linux build (busybox v1.29.3) as well
as my own (busybox v1.31.0.git-2019-01-02) build.

Attached is a file containing the relevant snippets from the tcpdump output for
both udhcpd and dnsmasq.

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