From e6d8b64b34aa8a9fe39609bc2db8a243b0331ceb Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 30 Oct 2013 11:50:52 +0100 Subject: net: sctp: fix and consolidate SCTP checksumming code This fixes an outstanding bug found through IPVS, where SCTP packets with skb->data_len > 0 (non-linearized) and empty frag_list, but data accumulated in frags[] member, are forwarded with incorrect checksum letting SCTP initial handshake fail on some systems. Linearizing each SCTP skb in IPVS to prevent that would not be a good solution as this leads to an additional and unnecessary performance penalty on the load-balancer itself for no good reason (as we actually only want to update the checksum, and can do that in a different/better way presented here). The actual problem is elsewhere, namely, that SCTP's checksumming in sctp_compute_cksum() does not take frags[] into account like skb_checksum() does. So while we are fixing this up, we better reuse the existing code that we have anyway in __skb_checksum() and use it for walking through the data doing checksumming. This will not only fix this issue, but also consolidates some SCTP code with core sk_buff code, bringing it closer together and removing respectively avoiding reimplementation of skb_checksum() for no good reason. As crc32c() can use hardware implementation within the crypto layer, we leave that intact (it wraps around / falls back to e.g. slice-by-8 algorithm in __crc32c_le() otherwise); plus use the __crc32c_le_combine() combinator for crc32c blocks. Also, we remove all other SCTP checksumming code, so that we only have to use sctp_compute_cksum() from now on; for doing that, we need to transform SCTP checkumming in output path slightly, and can leave the rest intact. Signed-off-by: Daniel Borkmann Signed-off-by: David S. Miller --- include/net/sctp/checksum.h | 56 +++++++++++++++------------------------------ 1 file changed, 19 insertions(+), 37 deletions(-) (limited to 'include/net/sctp') diff --git a/include/net/sctp/checksum.h b/include/net/sctp/checksum.h index 259924d..6bd44fe 100644 --- a/include/net/sctp/checksum.h +++ b/include/net/sctp/checksum.h @@ -42,56 +42,38 @@ #include #include #include +#include -static inline __u32 sctp_crc32c(__u32 crc, u8 *buffer, u16 length) +static inline __wsum sctp_csum_update(const void *buff, int len, __wsum sum) { - return crc32c(crc, buffer, length); -} - -static inline __u32 sctp_start_cksum(__u8 *buffer, __u16 length) -{ - __u32 crc = ~(__u32)0; - __u8 zero[sizeof(__u32)] = {0}; - - /* Optimize this routine to be SCTP specific, knowing how - * to skip the checksum field of the SCTP header. + /* This uses the crypto implementation of crc32c, which is either + * implemented w/ hardware support or resolves to __crc32c_le(). */ - - /* Calculate CRC up to the checksum. */ - crc = sctp_crc32c(crc, buffer, sizeof(struct sctphdr) - sizeof(__u32)); - - /* Skip checksum field of the header. */ - crc = sctp_crc32c(crc, zero, sizeof(__u32)); - - /* Calculate the rest of the CRC. */ - crc = sctp_crc32c(crc, &buffer[sizeof(struct sctphdr)], - length - sizeof(struct sctphdr)); - return crc; -} - -static inline __u32 sctp_update_cksum(__u8 *buffer, __u16 length, __u32 crc32) -{ - return sctp_crc32c(crc32, buffer, length); + return crc32c(sum, buff, len); } -static inline __le32 sctp_end_cksum(__u32 crc32) +static inline __wsum sctp_csum_combine(__wsum csum, __wsum csum2, + int offset, int len) { - return cpu_to_le32(~crc32); + return __crc32c_le_combine(csum, csum2, len); } -/* Calculate the CRC32C checksum of an SCTP packet. */ static inline __le32 sctp_compute_cksum(const struct sk_buff *skb, unsigned int offset) { - const struct sk_buff *iter; + struct sctphdr *sh = sctp_hdr(skb); + __le32 ret, old = sh->checksum; + const struct skb_checksum_ops ops = { + .update = sctp_csum_update, + .combine = sctp_csum_combine, + }; - __u32 crc32 = sctp_start_cksum(skb->data + offset, - skb_headlen(skb) - offset); - skb_walk_frags(skb, iter) - crc32 = sctp_update_cksum((__u8 *) iter->data, - skb_headlen(iter), crc32); + sh->checksum = 0; + ret = cpu_to_le32(~__skb_checksum(skb, offset, skb->len - offset, + ~(__u32)0, &ops)); + sh->checksum = old; - return sctp_end_cksum(crc32); + return ret; } #endif /* __sctp_checksum_h__ */ -- cgit v1.1