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netfilter: nf_conntrack_irc: Tighten matching on DCC message

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[ Upstream commit e8d5dfd1d8747b56077d02664a8838c71ced948e ]

CTCP messages should only be at the start of an IRC message, not
anywhere within it.

While the helper only decodes packes in the ORIGINAL direction, its
possible to make a client send a CTCP message back by empedding one into
a PING request.  As-is, thats enough to make the helper believe that it
saw a CTCP message.

Fixes: 869f37d8e4 ("[NETFILTER]: nf_conntrack/nf_nat: add IRC helper port")
Signed-off-by: David Leadbeater <dgl@dgl.cx>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
David Leadbeater 2022-08-26 14:56:57 +10:00 committed by Greg Kroah-Hartman
parent 369ec4dab0
commit 9a5d7e0acb
1 changed files with 28 additions and 6 deletions
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34
net/netfilter/nf_conntrack_irc.c
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@ -148,15 +148,37 @@ static int help(struct sk_buff *skb, unsigned int protoff,
data = ib_ptr;
data_limit = ib_ptr + skb->len - dataoff;
/* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
* 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
while (data < data_limit - (19 + MINMATCHLEN)) {
if (memcmp(data, "\1DCC ", 5)) {
/* Skip any whitespace */
while (data < data_limit - 10) {
if (*data == ' ' || *data == '\r' || *data == '\n')
data++;
else
break;
}
/* strlen("PRIVMSG x ")=10 */
if (data < data_limit - 10) {
if (strncasecmp("PRIVMSG ", data, 8))
goto out;
data += 8;
}
/* strlen(" :\1DCC SENT t AAAAAAAA P\1\n")=26
* 7+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=26
*/
while (data < data_limit - (21 + MINMATCHLEN)) {
/* Find first " :", the start of message */
if (memcmp(data, " :", 2)) {
data++;
continue;
}
data += 2;
/* then check that place only for the DCC command */
if (memcmp(data, "\1DCC ", 5))
goto out;
data += 5;
/* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
/* we have at least (21+MINMATCHLEN)-(2+5) bytes valid data left */
iph = ip_hdr(skb);
pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
@ -172,7 +194,7 @@ static int help(struct sk_buff *skb, unsigned int protoff,
pr_debug("DCC %s detected\n", dccprotos[i]);
/* we have at least
* (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
* (21+MINMATCHLEN)-7-dccprotos[i].matchlen bytes valid
* data left (== 14/13 bytes) */
if (parse_dcc(data, data_limit, &dcc_ip,
&dcc_port, &addr_beg_p, &addr_end_p)) {