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 <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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 <linux/types.h>
#include <net/sctp/sctp.h>
#include <linux/crc32c.h>
+#include <linux/crc32.h>
-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;
+ return crc32c(sum, buff, len);
}
-static inline __u32 sctp_update_cksum(__u8 *buffer, __u16 length, __u32 crc32)
+static inline __wsum sctp_csum_combine(__wsum csum, __wsum csum2,
+ int offset, int len)
{
- return sctp_crc32c(crc32, buffer, length);
+ return __crc32c_le_combine(csum, csum2, len);
}
-static inline __le32 sctp_end_cksum(__u32 crc32)
-{
- return cpu_to_le32(~crc32);
-}
-
-/* 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__ */