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linux_priv.c
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#include "config.h"
#include <seccomp.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <signal.h>
#include <string.h>
#include "memcached.h"
static char *kill_msg;
// Make sure to preserve the ??? position in the string, or correct the offsets
// in the syssig handler.
#define KILL_MSG_STR "Seccomp policy failure. Caught syscall ???. This is " \
"either an exploit attempt, or your system is not supported yet.\n"
static void handle_syssig(int signum, siginfo_t *si, void *thread_context) {
#if defined(si_syscall)
int syscall_no = si->si_syscall;
#else
// If system has no support for si_syscal, the information may not be
// precise.
int syscall_no = si->si_value.sival_int;
#endif
// Replace the characters in the kill message with the syscall number. We
// can't safely printf (even write is not really valid, but we're crashing
// anyway).
kill_msg[39] = (syscall_no / 100) % 10 + '0';
kill_msg[40] = (syscall_no / 10) % 10 + '0';
kill_msg[41] = syscall_no % 10 + '0';
if (write(2, kill_msg, strlen(kill_msg)) == -1) {
// An error occurred, but we can't do anything about it here. This check
// is mostly to avoid the "ignoring return value of 'write'" error on
// distributions with broken gcc (no "ignore via cast to void" support).
}
// We can't use the nice exit() version because it causes at_exit handlers
// to be looked up and run. We can't take any locks while handling the
// signal, so _exit() is the only thing to do safely.
_exit(EXIT_FAILURE);
}
static const struct sigaction act = {
.sa_sigaction = handle_syssig,
.sa_flags = SA_SIGINFO,
};
void setup_privilege_violations_handler(void) {
kill_msg = malloc(strlen(KILL_MSG_STR)+1);
strcpy(kill_msg, KILL_MSG_STR);
sigaction(SIGSYS, &act, NULL);
}
// If anything crosses the policy, kill the process.
#define DENY_ACTION SCMP_ACT_TRAP
void drop_privileges(void) {
scmp_filter_ctx ctx = seccomp_init(DENY_ACTION);
if (ctx == NULL) {
return;
}
int rc = 0;
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(sigreturn), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(rt_sigprocmask), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(futex), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(epoll_wait), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(epoll_pwait), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(accept4), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(accept), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(writev), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fstat), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mmap), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(munmap), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(shmctl), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit_group), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(brk), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1, SCMP_A1(SCMP_CMP_EQ, TIOCGWINSZ));
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1, SCMP_A1(SCMP_CMP_EQ, TCGETS));
#if defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(clock_gettime), 0);
#endif
#ifdef MEMCACHED_DEBUG
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(readv), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(lseek), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(close), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getpid), 0);
if (settings.relaxed_privileges) {
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(openat), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mkdir), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(access), 0);
}
#endif
if (rc != 0) {
goto fail;
}
rc = seccomp_load(ctx);
if (rc < 0) {
goto fail;
}
seccomp_release(ctx);
return;
fail:
seccomp_release(ctx);
fprintf(stderr, "Failed to set a seccomp profile on the main thread\n");
exit(EXIT_FAILURE);
}
void drop_worker_privileges(void) {
scmp_filter_ctx ctx = seccomp_init(DENY_ACTION);
if (ctx == NULL) {
return;
}
int rc = 0;
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(sigreturn), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(rt_sigprocmask), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(futex), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(epoll_wait), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(epoll_pwait), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(epoll_ctl), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(poll), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(readv), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mprotect), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getpeername), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(close), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(sendmsg), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getrusage), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mmap), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mremap), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(munmap), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(recvfrom), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(brk), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1, SCMP_A1(SCMP_CMP_EQ, TIOCGWINSZ));
// for spawning the LRU crawler
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(clone), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(set_robust_list), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(madvise), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit), 0);
// stat
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getsockname), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getpid), 0);
if (settings.shutdown_command) {
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(tgkill), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(tkill), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit_group), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fstat), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getpid), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(gettid), 0);
}
if (settings.relaxed_privileges) {
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(openat), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mkdir), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(access), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(lseek), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 0);
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(writev), 0);
} else {
// stdout
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1, SCMP_A0(SCMP_CMP_EQ, 1));
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(writev), 1, SCMP_A0(SCMP_CMP_EQ, 1));
// stderr
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1, SCMP_A0(SCMP_CMP_EQ, 2));
rc |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(writev), 1, SCMP_A0(SCMP_CMP_EQ, 2));
}
if (rc != 0) {
goto fail;
}
rc = seccomp_load(ctx);
if (rc < 0) {
goto fail;
}
seccomp_release(ctx);
return;
fail:
seccomp_release(ctx);
fprintf(stderr, "Failed to set a seccomp profile on a worker thread\n");
exit(EXIT_FAILURE);
}