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    Subject[PATCH 4.19 37/58] netfilter: nf_conntrack_irc: Tighten matching on DCC message
    Date
    From: David Leadbeater <dgl@dgl.cx>

    [ 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: 869f37d8e48f ("[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>
    ---
    net/netfilter/nf_conntrack_irc.c | 34 ++++++++++++++++++++++++++------
    1 file changed, 28 insertions(+), 6 deletions(-)

    diff --git a/net/netfilter/nf_conntrack_irc.c b/net/netfilter/nf_conntrack_irc.c
    index b7436935b57d..23ead02c6aa5 100644
    --- a/net/netfilter/nf_conntrack_irc.c
    +++ b/net/netfilter/nf_conntrack_irc.c
    @@ -150,15 +150,37 @@ 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",
    @@ -174,7 +196,7 @@ 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)) {
    --
    2.35.1


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