netfilter: nf_conntrack_irc: fix parse_dcc() off-by-one OOB read

netfilter: nf_conntrack_irc: fix parse_dcc() off-by-one OOB read

parse_dcc() treats data_end as an inclusive end pointer, but its only
caller passes data_limit = ib_ptr + datalen, which points one past the
last valid byte.

The newline search loop iterates while tmp <= data_end, so when no
newline is present, *tmp is read at tmp == data_end, one byte beyond
the region filled by skb_header_pointer().

irc_buffer is kmalloc'd as MAX_SEARCH_SIZE + 1 bytes and datalen is
capped at MAX_SEARCH_SIZE, so the stray read does not fault.  The byte
is uninitialized or stale; if it contains an ASCII digit, simple_strtoul
will consume it and produce a wrong DCC IP or port in the conntrack
expectation.  The extra allocation byte is also a fragile guard: if the
cap or allocation size changes, this becomes a real out-of-bounds read.

Change the loop and its post-loop check to use strict less-than,
consistent with the caller's exclusive-end convention.  Update the
function comment accordingly.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>