[IPX]: Annotate and fix IPX checksum
Calculation of IPX checksum got buggered about 2.4.0. The old variant
mangled the packet; that got fixed, but calculation itself got buggered.
Restored the correct logics, fixed a subtle breakage we used to have even
back then: if the sum is 0 mod 0xffff, we want to return 0, not 0xffff.
The latter has special meaning for IPX (cheksum disabled). Observation
(and obvious fix) nicked from history of FreeBSD ipx_cksum.c...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipx/af_ipx.c b/net/ipx/af_ipx.c
index c272a38a..76c6615 100644
--- a/net/ipx/af_ipx.c
+++ b/net/ipx/af_ipx.c
@@ -1234,27 +1234,27 @@
/* Note: We assume ipx_tctrl==0 and htons(length)==ipx_pktsize */
/* This functions should *not* mess with packet contents */
-__u16 ipx_cksum(struct ipxhdr *packet, int length)
+__be16 ipx_cksum(struct ipxhdr *packet, int length)
{
/*
* NOTE: sum is a net byte order quantity, which optimizes the
* loop. This only works on big and little endian machines. (I
* don't know of a machine that isn't.)
*/
- /* start at ipx_dest - We skip the checksum field and start with
- * ipx_type before the loop, not considering ipx_tctrl in the calc */
- __u16 *p = (__u16 *)&packet->ipx_dest;
- __u32 i = (length >> 1) - 1; /* Number of complete words */
- __u32 sum = packet->ipx_type << sizeof(packet->ipx_tctrl);
+ /* handle the first 3 words separately; checksum should be skipped
+ * and ipx_tctrl masked out */
+ __u16 *p = (__u16 *)packet;
+ __u32 sum = p[1] + (p[2] & (__force u16)htons(0x00ff));
+ __u32 i = (length >> 1) - 3; /* Number of remaining complete words */
- /* Loop through all complete words except the checksum field,
- * ipx_type (accounted above) and ipx_tctrl (not used in the cksum) */
- while (--i)
+ /* Loop through them */
+ p += 3;
+ while (i--)
sum += *p++;
/* Add on the last part word if it exists */
if (packet->ipx_pktsize & htons(1))
- sum += ntohs(0xff00) & *p;
+ sum += (__force u16)htons(0xff00) & *p;
/* Do final fixup */
sum = (sum & 0xffff) + (sum >> 16);
@@ -1263,7 +1263,14 @@
if (sum >= 0x10000)
sum++;
- return ~sum;
+ /*
+ * Leave 0 alone; we don't want 0xffff here. Note that we can't get
+ * here with 0x10000, so this check is the same as ((__u16)sum)
+ */
+ if (sum)
+ sum = ~sum;
+
+ return (__force __be16)sum;
}
const char *ipx_frame_name(__be16 frame)