From: Pablo Neira Ayuso Date: Thu, 6 Sep 2012 15:09:26 +0000 (+0200) Subject: netfilter: nfnetlink_queue: fix maximum packet length to userspace X-Git-Tag: firefly_0821_release~3680^2~1949^2~93^2~1 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ba8d3b0bf5900b9ee5354e7d73358867763a6766;p=firefly-linux-kernel-4.4.55.git netfilter: nfnetlink_queue: fix maximum packet length to userspace 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 Signed-off-by: Pablo Neira Ayuso --- diff --git a/net/netfilter/nfnetlink_queue_core.c b/net/netfilter/nfnetlink_queue_core.c index 43de3a03ee76..3e4ddcb7e781 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;