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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Jann Horn <jannh@google.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: [PATCH 3.18 12/24] tcp: dont read out-of-bounds opsize
Date: Fri, 27 Apr 2018 15:57:47 +0200	[thread overview]
Message-ID: <20180427135632.077528650@linuxfoundation.org> (raw)
In-Reply-To: <20180427135631.584839868@linuxfoundation.org>

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <jannh@google.com>


[ Upstream commit 7e5a206ab686f098367b61aca989f5cdfa8114a3 ]

The old code reads the "opsize" variable from out-of-bounds memory (first
byte behind the segment) if a broken TCP segment ends directly after an
opcode that is neither EOL nor NOP.

The result of the read isn't used for anything, so the worst thing that
could theoretically happen is a pagefault; and since the physmap is usually
mostly contiguous, even that seems pretty unlikely.

The following C reproducer triggers the uninitialized read - however, you
can't actually see anything happen unless you put something like a
pr_warn() in tcp_parse_md5sig_option() to print the opsize.

====================================
#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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_input.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3731,11 +3731,8 @@ const u8 *tcp_parse_md5sig_option(const
 	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;
 

  parent reply	other threads:[~2018-04-27 13:58 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-27 13:57 [PATCH 3.18 00/24] 3.18.107-stable review Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 01/24] cifs: do not allow creating sockets except with SMB1 posix exensions Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 02/24] x86/tsc: Prevent 32bit truncation in calc_hpet_ref() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 03/24] ext4: fix deadlock between inline_data and ext4_expand_extra_isize_ea() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 04/24] ext4: bugfix for mmaped pages in mpage_release_unused_pages() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 05/24] ext4: dont update checksum of new initialized bitmaps Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 06/24] perf: Return proper values for user stack errors Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 07/24] mm/filemap.c: fix NULL pointer in page_cache_tree_insert() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 08/24] jbd2: fix use after free in kjournald2() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 09/24] bonding: do not set slave_dev npinfo before slave_enable_netpoll in bond_enslave Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 10/24] KEYS: DNS: limit the length of option strings Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 11/24] l2tp: check sockaddr length in pppol2tp_connect() Greg Kroah-Hartman
2018-04-27 13:57 ` Greg Kroah-Hartman [this message]
2018-04-27 13:57 ` [PATCH 3.18 13/24] team: avoid adding twice the same option to the event list Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 14/24] team: fix netconsole setup over team Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 15/24] pppoe: check sockaddr length in pppoe_connect() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 16/24] llc: hold llc_sap before release_sock() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 17/24] llc: fix NULL pointer deref for SOCK_ZAPPED Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 18/24] packet: fix bitfield update race Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 19/24] tcp: md5: reject TCP_MD5SIG or TCP_MD5SIG_EXT on established sockets Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 20/24] net: af_packet: fix race in PACKET_{R|T}X_RING Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 21/24] llc: delete timers synchronously in llc_sk_free() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 22/24] ipv6: add RTA_TABLE and RTA_PREFSRC to rtm_ipv6_policy Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 23/24] scsi: mptsas: Disable WRITE SAME Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 3.18 24/24] cdrom: information leak in cdrom_ioctl_media_changed() Greg Kroah-Hartman
2018-04-27 16:00 ` [PATCH 3.18 00/24] 3.18.107-stable review Dede Dindin Qudsy
2018-04-28  5:51   ` Greg Kroah-Hartman
2018-04-28  6:40     ` Harsh Shandilya
2018-04-27 18:12 ` Shuah Khan
2018-04-28  5:02   ` Greg Kroah-Hartman
2018-04-27 19:03 ` kernelci.org bot
2018-04-27 19:41 ` Theodore Y. Ts'o
2018-04-28  4:35   ` Greg Kroah-Hartman
2018-04-27 21:33 ` Harsh Shandilya
2018-04-28  5:02   ` Greg Kroah-Hartman
2018-04-28 14:24 ` Guenter Roeck

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