Date: Fri, 05 Aug 2011 19:29:42 +0200 From: Andre Oppermann <andre@freebsd.org> To: Matthew Cini Sarreo <mcins1@gmail.com> Cc: freebsd-net@freebsd.org Subject: Re: ESP Raw Socket: Returned IP packet incorrect Message-ID: <4E3C2886.9070100@freebsd.org> In-Reply-To: <CAFj3ReT6mmT6ScWf-FBT-1%2BF8z9PWHyFj-R7haWvaV-bq=42PQ@mail.gmail.com> References: <CAFj3ReT6mmT6ScWf-FBT-1%2BF8z9PWHyFj-R7haWvaV-bq=42PQ@mail.gmail.com>
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On 11.07.2011 17:26, Matthew Cini Sarreo wrote: > Hello all; > > I have recently encountered a problem when using raw sockets on FreeBSD 8 > (8.0-RELEASE) when using ESP raw sockets. > > I have created a raw esp socket using: > socket(AF_INET, SOCK_RAW, 50); > which works fine. However, when there is a packet on the socket, recvfrom() > returns a packet where the length bytes in the IP header are incorrect; they > are swapped (MSB is placed in the LSB and vice-versa) > > tcpdump shows the following: > > tcpdump: listening on le0, link-type EN10MB (Ethernet), capture size 96 > bytes > 15:00:53.993810 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ESP > (50), length 120) > 10.0.251.228> 10.0.252.231: ESP(spi=0xa0534f17,seq=0x3), length 100 > 0x0000: 4500 0078 0000 4000 4032 2d88 0a00 fbe4 > 0x0010: 0a00 fce7 a053 4f17 0000 0003 6885 8abd > 0x0020: 2222 5ded 44dc 842f 3081 8fa3 bde4 2265 > 0x0030: 7438 2bf4 049c 664b 7dc4 44ef 1f6f 5e7d > 0x0040: b8c1 482f 8c3b f488 a19a 3d9a d5fe ed9d > 0x0050: b1c2 > > > However, recvfrom() returns the following buffer: > 4500 6400 0000 0040 4032 2D88 0A00 FBE4 > 0A00 FCE7 A053 4F17 0000 0003 6885 8ABD > 2222 5DED 44DC 842F 3081 8FA3 BDE4 2265 > 7438 2BF4 049C 664B 7DC4 44EF 1F6F 5E7D > B8C1 482F 8C3B F488 A19A 3D9A D5FE ED9D > B1C2 > > As it is easy to see, the length is not correct (bytes 2 and 3 are 0x6400 > instead of 0x0064) and it does not correspond to the value returned by > recvfrom(). > > Is this a known issue? Am I missing some options for raw sockets that are > required for FreeBSD? I have attempted this on a socket to a TUN interface > (not with an ESP socket) and the buffer had the proper length; it seems to > only happen with ESP. This code runs fine on multiple Linux distributions > and on Windows; it was only noticed with FreeBSD. Could it be that there is > some other ESP application running and interfering (I have not installed > any; don't know if there are by default and I'm quite new to any of the > BSDs)? The problem is with all raw sockets. Contrary to the statement in ip(4) "Incoming packets are received with IP header and options intact" and other popular OSes the ip_len field in the IP header has the IP header length already deducted (line 770 in ip_input.c). For normal in-kernel implemented protocols this is fine but raw sockets it is clearly wrong. The fix is pretty easy and just adds the header length back in raw_input() in raw_ip.c. Please test this patch: http://people.freebsd.org/~andre/raw_ip-header-length-20110805.diff -- Andre
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