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xen-netback: fix fragment detection in checksum setup
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The code to detect fragments in checksum_setup() was missing for IPv4 and
too eager for IPv6. (It transpires that Windows seems to send IPv6 packets
with a fragment header even if they are not a fragment - i.e. offset is zero,
and M bit is not set).

This patch also incorporates a fix to callers of maybe_pull_tail() where
skb->network_header was being erroneously added to the length argument.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
cc: David Miller <davem@davemloft.net>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Paul Durrant authored and David S. Miller committed Dec 6, 2013
1 parent df48ada commit 1431fb3
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Showing 3 changed files with 140 additions and 100 deletions.
236 changes: 137 additions & 99 deletions drivers/net/xen-netback/netback.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1149,49 +1149,72 @@ static int xenvif_set_skb_gso(struct xenvif *vif,
return 0;
}

static inline void maybe_pull_tail(struct sk_buff *skb, unsigned int len)
static inline int maybe_pull_tail(struct sk_buff *skb, unsigned int len,
unsigned int max)
{
if (skb_is_nonlinear(skb) && skb_headlen(skb) < len) {
/* If we need to pullup then pullup to the max, so we
* won't need to do it again.
*/
int target = min_t(int, skb->len, MAX_TCP_HEADER);
__pskb_pull_tail(skb, target - skb_headlen(skb));
}
if (skb_headlen(skb) >= len)
return 0;

/* If we need to pullup then pullup to the max, so we
* won't need to do it again.
*/
if (max > skb->len)
max = skb->len;

if (__pskb_pull_tail(skb, max - skb_headlen(skb)) == NULL)
return -ENOMEM;

if (skb_headlen(skb) < len)
return -EPROTO;

return 0;
}

/* This value should be large enough to cover a tagged ethernet header plus
* maximally sized IP and TCP or UDP headers.
*/
#define MAX_IP_HDR_LEN 128

static int checksum_setup_ip(struct xenvif *vif, struct sk_buff *skb,
int recalculate_partial_csum)
{
struct iphdr *iph = (void *)skb->data;
unsigned int header_size;
unsigned int off;
int err = -EPROTO;
bool fragment;
int err;

fragment = false;

err = maybe_pull_tail(skb,
sizeof(struct iphdr),
MAX_IP_HDR_LEN);
if (err < 0)
goto out;

off = sizeof(struct iphdr);
if (ip_hdr(skb)->frag_off & htons(IP_OFFSET | IP_MF))
fragment = true;

header_size = skb->network_header + off + MAX_IPOPTLEN;
maybe_pull_tail(skb, header_size);
off = ip_hdrlen(skb);

off = iph->ihl * 4;
err = -EPROTO;

switch (iph->protocol) {
switch (ip_hdr(skb)->protocol) {
case IPPROTO_TCP:
if (!skb_partial_csum_set(skb, off,
offsetof(struct tcphdr, check)))
goto out;

if (recalculate_partial_csum) {
struct tcphdr *tcph = tcp_hdr(skb);

header_size = skb->network_header +
off +
sizeof(struct tcphdr);
maybe_pull_tail(skb, header_size);

tcph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
skb->len - off,
IPPROTO_TCP, 0);
err = maybe_pull_tail(skb,
off + sizeof(struct tcphdr),
MAX_IP_HDR_LEN);
if (err < 0)
goto out;

tcp_hdr(skb)->check =
~csum_tcpudp_magic(ip_hdr(skb)->saddr,
ip_hdr(skb)->daddr,
skb->len - off,
IPPROTO_TCP, 0);
}
break;
case IPPROTO_UDP:
Expand All @@ -1200,24 +1223,20 @@ static int checksum_setup_ip(struct xenvif *vif, struct sk_buff *skb,
goto out;

if (recalculate_partial_csum) {
struct udphdr *udph = udp_hdr(skb);

header_size = skb->network_header +
off +
sizeof(struct udphdr);
maybe_pull_tail(skb, header_size);

udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
skb->len - off,
IPPROTO_UDP, 0);
err = maybe_pull_tail(skb,
off + sizeof(struct udphdr),
MAX_IP_HDR_LEN);
if (err < 0)
goto out;

udp_hdr(skb)->check =
~csum_tcpudp_magic(ip_hdr(skb)->saddr,
ip_hdr(skb)->daddr,
skb->len - off,
IPPROTO_UDP, 0);
}
break;
default:
if (net_ratelimit())
netdev_err(vif->dev,
"Attempting to checksum a non-TCP/UDP packet, "
"dropping a protocol %d packet\n",
iph->protocol);
goto out;
}

Expand All @@ -1227,75 +1246,99 @@ static int checksum_setup_ip(struct xenvif *vif, struct sk_buff *skb,
return err;
}

/* This value should be large enough to cover a tagged ethernet header plus
* an IPv6 header, all options, and a maximal TCP or UDP header.
*/
#define MAX_IPV6_HDR_LEN 256

#define OPT_HDR(type, skb, off) \
(type *)(skb_network_header(skb) + (off))

static int checksum_setup_ipv6(struct xenvif *vif, struct sk_buff *skb,
int recalculate_partial_csum)
{
int err = -EPROTO;
struct ipv6hdr *ipv6h = (void *)skb->data;
int err;
u8 nexthdr;
unsigned int header_size;
unsigned int off;
unsigned int len;
bool fragment;
bool done;

fragment = false;
done = false;

off = sizeof(struct ipv6hdr);

header_size = skb->network_header + off;
maybe_pull_tail(skb, header_size);
err = maybe_pull_tail(skb, off, MAX_IPV6_HDR_LEN);
if (err < 0)
goto out;

nexthdr = ipv6h->nexthdr;
nexthdr = ipv6_hdr(skb)->nexthdr;

while ((off <= sizeof(struct ipv6hdr) + ntohs(ipv6h->payload_len)) &&
!done) {
len = sizeof(struct ipv6hdr) + ntohs(ipv6_hdr(skb)->payload_len);
while (off <= len && !done) {
switch (nexthdr) {
case IPPROTO_DSTOPTS:
case IPPROTO_HOPOPTS:
case IPPROTO_ROUTING: {
struct ipv6_opt_hdr *hp = (void *)(skb->data + off);
struct ipv6_opt_hdr *hp;

header_size = skb->network_header +
off +
sizeof(struct ipv6_opt_hdr);
maybe_pull_tail(skb, header_size);
err = maybe_pull_tail(skb,
off +
sizeof(struct ipv6_opt_hdr),
MAX_IPV6_HDR_LEN);
if (err < 0)
goto out;

hp = OPT_HDR(struct ipv6_opt_hdr, skb, off);
nexthdr = hp->nexthdr;
off += ipv6_optlen(hp);
break;
}
case IPPROTO_AH: {
struct ip_auth_hdr *hp = (void *)(skb->data + off);
struct ip_auth_hdr *hp;

err = maybe_pull_tail(skb,
off +
sizeof(struct ip_auth_hdr),
MAX_IPV6_HDR_LEN);
if (err < 0)
goto out;

hp = OPT_HDR(struct ip_auth_hdr, skb, off);
nexthdr = hp->nexthdr;
off += ipv6_authlen(hp);
break;
}
case IPPROTO_FRAGMENT: {
struct frag_hdr *hp;

header_size = skb->network_header +
off +
sizeof(struct ip_auth_hdr);
maybe_pull_tail(skb, header_size);
err = maybe_pull_tail(skb,
off +
sizeof(struct frag_hdr),
MAX_IPV6_HDR_LEN);
if (err < 0)
goto out;

hp = OPT_HDR(struct frag_hdr, skb, off);

if (hp->frag_off & htons(IP6_OFFSET | IP6_MF))
fragment = true;

nexthdr = hp->nexthdr;
off += (hp->hdrlen+2)<<2;
off += sizeof(struct frag_hdr);
break;
}
case IPPROTO_FRAGMENT:
fragment = true;
/* fall through */
default:
done = true;
break;
}
}

if (!done) {
if (net_ratelimit())
netdev_err(vif->dev, "Failed to parse packet header\n");
goto out;
}
err = -EPROTO;

if (fragment) {
if (net_ratelimit())
netdev_err(vif->dev, "Packet is a fragment!\n");
if (!done || fragment)
goto out;
}

switch (nexthdr) {
case IPPROTO_TCP:
Expand All @@ -1304,17 +1347,17 @@ static int checksum_setup_ipv6(struct xenvif *vif, struct sk_buff *skb,
goto out;

if (recalculate_partial_csum) {
struct tcphdr *tcph = tcp_hdr(skb);

header_size = skb->network_header +
off +
sizeof(struct tcphdr);
maybe_pull_tail(skb, header_size);

tcph->check = ~csum_ipv6_magic(&ipv6h->saddr,
&ipv6h->daddr,
skb->len - off,
IPPROTO_TCP, 0);
err = maybe_pull_tail(skb,
off + sizeof(struct tcphdr),
MAX_IPV6_HDR_LEN);
if (err < 0)
goto out;

tcp_hdr(skb)->check =
~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
&ipv6_hdr(skb)->daddr,
skb->len - off,
IPPROTO_TCP, 0);
}
break;
case IPPROTO_UDP:
Expand All @@ -1323,25 +1366,20 @@ static int checksum_setup_ipv6(struct xenvif *vif, struct sk_buff *skb,
goto out;

if (recalculate_partial_csum) {
struct udphdr *udph = udp_hdr(skb);

header_size = skb->network_header +
off +
sizeof(struct udphdr);
maybe_pull_tail(skb, header_size);

udph->check = ~csum_ipv6_magic(&ipv6h->saddr,
&ipv6h->daddr,
skb->len - off,
IPPROTO_UDP, 0);
err = maybe_pull_tail(skb,
off + sizeof(struct udphdr),
MAX_IPV6_HDR_LEN);
if (err < 0)
goto out;

udp_hdr(skb)->check =
~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
&ipv6_hdr(skb)->daddr,
skb->len - off,
IPPROTO_UDP, 0);
}
break;
default:
if (net_ratelimit())
netdev_err(vif->dev,
"Attempting to checksum a non-TCP/UDP packet, "
"dropping a protocol %d packet\n",
nexthdr);
goto out;
}

Expand Down
1 change: 1 addition & 0 deletions include/linux/ipv6.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
#include <uapi/linux/ipv6.h>

#define ipv6_optlen(p) (((p)->hdrlen+1) << 3)
#define ipv6_authlen(p) (((p)->hdrlen+2) << 2)
/*
* This structure contains configuration options per IPv6 link.
*/
Expand Down
3 changes: 2 additions & 1 deletion include/net/ipv6.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -110,7 +110,8 @@ struct frag_hdr {
__be32 identification;
};

#define IP6_MF 0x0001
#define IP6_MF 0x0001
#define IP6_OFFSET 0xFFF8

#include <net/sock.h>

Expand Down

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