Commit 02e60370 authored by Al Viro's avatar Al Viro Committed by David S. Miller
Browse files

[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: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4833ed09

include/net/ipx.h

+2 −2
Original line number Diff line number Diff line
@@ -26,8 +26,8 @@ struct ipx_address { 
#define IPX_MAX_PPROP_HOPS 8



struct ipxhdr {

	__u16			ipx_checksum __attribute__ ((packed));

#define IPX_NO_CHECKSUM	0xFFFF

	__be16			ipx_checksum __attribute__ ((packed));

#define IPX_NO_CHECKSUM	__constant_htons(0xFFFF)

	__be16			ipx_pktsize __attribute__ ((packed));

	__u8			ipx_tctrl;

	__u8			ipx_type;

net/ipx/af_ipx.c

+19 −12
Original line number Diff line number Diff line
@@ -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 */

/* 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); 



	/* Loop through all complete words except the checksum field,

	 * ipx_type (accounted above) and ipx_tctrl (not used in the cksum) */

	while (--i)

	/* 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 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 @@ __u16 ipx_cksum(struct ipxhdr *packet, int length) 
	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)

net/ipx/ipx_route.c

+2 −2
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ DEFINE_RWLOCK(ipx_routes_lock); 


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 int ipxitf_demux_socket(struct ipx_interface *intrfc,

			       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. */

	if (sk->sk_no_check || intrfc->if_dlink_type == htons(IPX_FRAME_8023))

		ipx->ipx_checksum = 0xFFFF;

		ipx->ipx_checksum = htons(0xFFFF);

	else

		ipx->ipx_checksum = ipx_cksum(ipx, len + sizeof(struct ipxhdr));

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