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[IPX]: Annotate and fix IPX checksum

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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>
This commit is contained in:
Al Viro 2006-11-03 00:28:23 -08:00 committed by David S. Miller
parent 4833ed0940
commit 02e60370d4
3 changed files with 22 additions and 15 deletions
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4
include/net/ipx.h
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@ -26,8 +26,8 @@ struct ipx_address {
#define IPX_MAX_PPROP_HOPS 8 #define IPX_MAX_PPROP_HOPS 8
struct ipxhdr { struct ipxhdr {
__u16 ipx_checksum __attribute__ ((packed)); __be16 ipx_checksum __attribute__ ((packed));
#define IPX_NO_CHECKSUM 0xFFFF #define IPX_NO_CHECKSUM __constant_htons(0xFFFF)
__be16 ipx_pktsize __attribute__ ((packed)); __be16 ipx_pktsize __attribute__ ((packed));
__u8 ipx_tctrl; __u8 ipx_tctrl;
__u8 ipx_type; __u8 ipx_type;

29
net/ipx/af_ipx.c
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@ -1234,27 +1234,27 @@ static int ipxitf_ioctl(unsigned int cmd, void __user *arg)
/* Note: We assume ipx_tctrl==0 and htons(length)==ipx_pktsize */ /* Note: We assume ipx_tctrl==0 and htons(length)==ipx_pktsize */
/* This functions should *not* mess with packet contents */ /* 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 * NOTE: sum is a net byte order quantity, which optimizes the
* loop. This only works on big and little endian machines. (I * loop. This only works on big and little endian machines. (I
* don't know of a machine that isn't.) * don't know of a machine that isn't.)
*/ */
/* start at ipx_dest - We skip the checksum field and start with /* handle the first 3 words separately; checksum should be skipped
* ipx_type before the loop, not considering ipx_tctrl in the calc */ * and ipx_tctrl masked out */
__u16 *p = (__u16 *)&packet->ipx_dest; __u16 *p = (__u16 *)packet;
__u32 i = (length >> 1) - 1; /* Number of complete words */ __u32 sum = p[1] + (p[2] & (__force u16)htons(0x00ff));
__u32 sum = packet->ipx_type << sizeof(packet->ipx_tctrl); __u32 i = (length >> 1) - 3; /* Number of remaining complete words */
/* Loop through all complete words except the checksum field, /* Loop through them */
* ipx_type (accounted above) and ipx_tctrl (not used in the cksum) */ p += 3;
while (--i) while (i--)
sum += *p++; sum += *p++;
/* Add on the last part word if it exists */ /* Add on the last part word if it exists */
if (packet->ipx_pktsize & htons(1)) if (packet->ipx_pktsize & htons(1))
sum += ntohs(0xff00) & *p; sum += (__force u16)htons(0xff00) & *p;
/* Do final fixup */ /* Do final fixup */
sum = (sum & 0xffff) + (sum >> 16); sum = (sum & 0xffff) + (sum >> 16);
@ -1263,7 +1263,14 @@ __u16 ipx_cksum(struct ipxhdr *packet, int length)
if (sum >= 0x10000) if (sum >= 0x10000)
sum++; 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) const char *ipx_frame_name(__be16 frame)

4
net/ipx/ipx_route.c
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@ -19,7 +19,7 @@ DEFINE_RWLOCK(ipx_routes_lock);
extern struct ipx_interface *ipx_internal_net; extern struct ipx_interface *ipx_internal_net;
extern __u16 ipx_cksum(struct ipxhdr *packet, int length); extern __be16 ipx_cksum(struct ipxhdr *packet, int length);
extern struct ipx_interface *ipxitf_find_using_net(__be32 net); extern struct ipx_interface *ipxitf_find_using_net(__be32 net);
extern int ipxitf_demux_socket(struct ipx_interface *intrfc, extern int ipxitf_demux_socket(struct ipx_interface *intrfc,
struct sk_buff *skb, int copy); struct sk_buff *skb, int copy);
@ -238,7 +238,7 @@ int ipxrtr_route_packet(struct sock *sk, struct sockaddr_ipx *usipx,
/* Apply checksum. Not allowed on 802.3 links. */ /* Apply checksum. Not allowed on 802.3 links. */
if (sk->sk_no_check || intrfc->if_dlink_type == htons(IPX_FRAME_8023)) if (sk->sk_no_check || intrfc->if_dlink_type == htons(IPX_FRAME_8023))
ipx->ipx_checksum = 0xFFFF; ipx->ipx_checksum = htons(0xFFFF);
else else
ipx->ipx_checksum = ipx_cksum(ipx, len + sizeof(struct ipxhdr)); ipx->ipx_checksum = ipx_cksum(ipx, len + sizeof(struct ipxhdr));