From: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> The packets that we send via NFQUEUE are encapsulated in the NFQA_PAYLOAD attribute. The length of the packet in userspace is obtained via attr->nla_len field. This field contains the size of the Netlink attribute header plus the packet length. If the maximum packet length is specified, ie. 65535 bytes, and packets in the range of (65531,65535] are sent to userspace, the attr->nla_len overflows and it reports bogus lengths to the application. To fix this, this patch limits the maximum packet length to 65531 bytes. If larger packet length is specified, the packet that we send to user-space is truncated to 65531 bytes. To support 65535 bytes packets, we have to revisit the idea of the 32-bits Netlink attribute length. Reported-by: Florian Westphal <fw@xxxxxxxxx> Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> --- net/netfilter/nfnetlink_queue_core.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/net/netfilter/nfnetlink_queue_core.c b/net/netfilter/nfnetlink_queue_core.c index 43de3a0..3e4ddcb7 100644 --- a/net/netfilter/nfnetlink_queue_core.c +++ b/net/netfilter/nfnetlink_queue_core.c @@ -526,9 +526,13 @@ nfqnl_set_mode(struct nfqnl_instance *queue, case NFQNL_COPY_PACKET: queue->copy_mode = mode; - /* we're using struct nlattr which has 16bit nla_len */ - if (range > 0xffff) - queue->copy_range = 0xffff; + /* We're using struct nlattr which has 16bit nla_len. Note that + * nla_len includes the header length. Thus, the maximum packet + * length that we support is 65531 bytes. We send truncated + * packets if the specified length is larger than that. + */ + if (range > 0xffff - NLA_HDRLEN) + queue->copy_range = 0xffff - NLA_HDRLEN; else queue->copy_range = range; break; -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
