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fix(tools): stop unsandboxed shell hang after output cap #69

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fix(tools): stop unsandboxed shell hang after output cap #69

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69 changes: 57 additions & 12 deletions src/tools/shell.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,12 +19,14 @@
#include "sandbox/sandbox.h"
#include "sandbox/allowlist.h"
#include "cJSON.h"
#include <errno.h>
#include <poll.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#define DEFAULT_TIMEOUT_SEC 60
Expand Down Expand Up @@ -56,6 +58,49 @@ static int fallback_is_blocked(const char *cmd)

static const config_t *g_shell_cfg;

static void kill_command_tree(pid_t pid)
{
if (kill(-pid, SIGKILL) != 0)
(void)kill(pid, SIGKILL);
}

/* Kill leftover children after drain (timeout or output cap), matching sandbox_exec. */
static int reap_running_child(pid_t pid)
{
int status = 0;
int wr = waitpid(pid, &status, WNOHANG);
int i;
struct timespec ts;

if (wr != 0)
return 0;
kill_command_tree(pid);
for (i = 0; i < 40; i++) {
wr = waitpid(pid, &status, WNOHANG);
if (wr != 0)
return 1;
ts.tv_sec = 0;
ts.tv_nsec = 50 * 1000 * 1000;
(void)nanosleep(&ts, NULL);
}
(void)waitpid(pid, &status, 0);
return 1;
}

static void append_unsandboxed_output(char *result_buf, size_t max_len, size_t *total,
const char *chunk, size_t n)
{
size_t add = n;

if (*total + add >= max_len - 1)
add = max_len - 1 - *total;
if (add == 0)
return;
memcpy(result_buf + *total, chunk, add);
*total += add;
result_buf[*total] = '\0';
}

/* ------------------------------------------------------------------ */
/* Unsandboxed execution (fork + poll + waitpid) */
/* ------------------------------------------------------------------ */
Expand All @@ -68,7 +113,6 @@ static int run_unsandboxed(const char *command, int timeout_sec,
size_t total = 0;
int timed_out = 0;
int elapsed_ms = 0;
int status;
char buf[256];
if (pipe(pipefd) != 0) {
snprintf(result_buf, max_len, "{\"error\":\"pipe failed\"}");
Expand All @@ -86,9 +130,11 @@ static int run_unsandboxed(const char *command, int timeout_sec,
dup2(pipefd[1], STDOUT_FILENO);
dup2(pipefd[1], STDERR_FILENO);
close(pipefd[1]);
(void)setpgid(0, 0);
execl("/bin/sh", "sh", "-c", command, (char *)NULL);
_exit(127);
}
(void)setpgid(pid, pid);
close(pipefd[1]);
result_buf[0] = '\0';
while (total < max_len - 1 && elapsed_ms < timeout_sec * 1000) {
Expand All @@ -102,28 +148,27 @@ static int run_unsandboxed(const char *command, int timeout_sec,
rem = timeout_sec * 1000 - elapsed_ms;
if (rem > 5000) rem = 5000;
r = poll(&pfd, 1, rem);
if (r < 0) break;
if (r < 0) {
if (errno == EINTR) continue;
break;
}
if (r == 0) {
elapsed_ms += rem;
if (elapsed_ms >= timeout_sec * 1000) {
timed_out = 1;
kill(pid, SIGKILL);
kill_command_tree(pid);
break;
}
continue;
}
n = read(pipefd[0], buf, sizeof(buf) - 1);
n = read(pipefd[0], buf, sizeof(buf));
if (n <= 0) break;
buf[n] = '\0';
{
size_t add = (size_t)n;
if (total + add >= max_len - 1) add = max_len - 1 - total;
memcpy(result_buf + total, buf, add + 1);
total += add;
}
append_unsandboxed_output(result_buf, max_len, &total, buf, (size_t)n);
}
result_buf[total] = '\0';
close(pipefd[0]);
waitpid(pid, &status, 0);
if (reap_running_child(pid))
timed_out = 1;
if (timed_out && total < max_len - 32)
snprintf(result_buf + total, max_len - total, "\n[Command timed out]");
return 0;
Expand Down
44 changes: 44 additions & 0 deletions tests/test_shell.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,11 @@
#include "tools/tool.h"
#include "tools/shell.h"
#include "core/config.h"
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static int tests_run = 0;
static int tests_failed = 0;
Expand Down Expand Up @@ -68,13 +71,54 @@ static void test_shell_missing_command(void)
MU_ASSERT(r == -1, "missing command returns -1");
}

static void output_cap_hang_watchdog(int sig)
{
(void)sig;
fprintf(stderr, "FAIL: unsandboxed shell hung after filling the output cap\n");
_exit(2);
}

static int buf_has_nul(const char *buf, size_t n)
{
size_t i;

for (i = 0; i < n; i++) {
if (buf[i] == '\0')
return 1;
}
return 0;
}

static void test_shell_caps_output_without_hanging(void)
{
const tool_t *t = tool_shell_get();
char buf[64];
int r;

tool_shell_set_config(NULL);
memset(buf, 'B', sizeof(buf));
signal(SIGALRM, output_cap_hang_watchdog);
alarm(5);
/* Fill the 64-byte cap, then sleep so the child stays alive without
* writing (SIGPIPE will not reap it). Unsandboxed waitpid used to block
* forever on this path.
*/
r = t->execute("{\"command\":\"printf '%080d' 0; sleep 9999\"}", buf,
sizeof(buf));
alarm(0);
signal(SIGALRM, SIG_DFL);
MU_ASSERT(r == 0, "capped shell command returns");
MU_ASSERT(buf_has_nul(buf, sizeof(buf)), "capped output is NUL-terminated");
}

int main(void)
{
MU_RUN(test_shell_blocked_rm_rf);
MU_RUN(test_shell_blocked_mkfs);
MU_RUN(test_shell_ls_succeeds);
MU_RUN(test_shell_invalid_json);
MU_RUN(test_shell_missing_command);
MU_RUN(test_shell_caps_output_without_hanging);
printf("%d tests run, %d failed\n", tests_run, tests_failed);
return tests_failed ? 1 : 0;
}
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