/**
* Function responsible for setting up the socket syscall for
* the seccomp filter sandbox.
*/
static int
sb_socket(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
{
int rc = 0;
int i, j;
(void) filter;
#ifdef __i386__
rc = seccomp_rule_add_0(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket));
if (rc)
return rc;
#endif
rc = seccomp_rule_add_2(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_FILE),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_STREAM));
if (rc)
return rc;
for (i = 0; i < 2; ++i) {
const int pf = i ? PF_INET : PF_INET6;
for (j=0; j < 3; ++j) {
const int type = (j == 0) ? SOCK_STREAM :
SOCK_DGRAM;
const int protocol = (j == 0) ? IPPROTO_TCP :
(j == 1) ? IPPROTO_IP :
IPPROTO_UDP;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, pf),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, type),
SCMP_CMP(2, SCMP_CMP_EQ, protocol));
if (rc)
return rc;
}
}
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_UNIX),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_STREAM),
SCMP_CMP(2, SCMP_CMP_EQ, 0));
if (rc)
return rc;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_UNIX),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_DGRAM),
SCMP_CMP(2, SCMP_CMP_EQ, 0));
if (rc)
return rc;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_NETLINK),
SCMP_CMP(1, SCMP_CMP_EQ, SOCK_RAW),
SCMP_CMP(2, SCMP_CMP_EQ, 0));
if (rc)
return rc;
return 0;
}
/**
* Function responsible for setting up the openat syscall for
* the seccomp filter sandbox.
*/
static int
sb_openat(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
{
int rc;
sandbox_cfg_t *elem = NULL;
// for each dynamic parameter filters
for (elem = filter; elem != NULL; elem = elem->next) {
smp_param_t *param = elem->param;
if (param != NULL && param->prot == 1 && param->syscall
== SCMP_SYS(openat)) {
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(openat),
SCMP_CMP(0, SCMP_CMP_EQ, AT_FDCWD),
SCMP_CMP_STR(1, SCMP_CMP_EQ, param->value),
SCMP_CMP(2, SCMP_CMP_EQ, O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|
O_CLOEXEC));
if (rc != 0) {
log_err(LD_BUG,"(Sandbox) failed to add openat syscall, received "
"libseccomp error %d", rc);
return rc;
}
}
}
return 0;
}
/**
* Function responsible for setting up the socket syscall for
* the seccomp filter sandbox.
*/
static int
sb_socket(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
{
int rc = 0;
int i;
(void) filter;
#ifdef __i386__
rc = seccomp_rule_add_0(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket));
if (rc)
return rc;
#endif
rc = seccomp_rule_add_2(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_FILE),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_STREAM));
if (rc)
return rc;
for (i = 0; i < 2; ++i) {
const int pf = i ? PF_INET : PF_INET6;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, pf),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_STREAM),
SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_TCP));
if (rc)
return rc;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, pf),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_DGRAM),
SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_IP));
if (rc)
return rc;
}
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_NETLINK),
SCMP_CMP(1, SCMP_CMP_EQ, SOCK_RAW),
SCMP_CMP(2, SCMP_CMP_EQ, 0));
if (rc)
return rc;
return 0;
}
/**
* Protects all the strings in the sandbox's parameter list configuration. It
* works by calculating the total amount of memory required by the parameter
* list, allocating the memory using mmap, and protecting it from writes with
* mprotect().
*/
static int
prot_strings(scmp_filter_ctx ctx, sandbox_cfg_t* cfg)
{
int ret = 0;
size_t pr_mem_size = 0, pr_mem_left = 0;
char *pr_mem_next = NULL, *pr_mem_base;
sandbox_cfg_t *el = NULL;
strmap_t *locations = NULL;
// get total number of bytes required to mmap. (Overestimate.)
for (el = cfg; el != NULL; el = el->next) {
pr_mem_size += strlen((char*) el->param->value) + 1;
if (el->param->value2)
pr_mem_size += strlen((char*) el->param->value2) + 1;
}
// allocate protected memory with MALLOC_MP_LIM canary
pr_mem_base = (char*) mmap(NULL, MALLOC_MP_LIM + pr_mem_size,
PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
if (pr_mem_base == MAP_FAILED) {
log_err(LD_BUG,"(Sandbox) failed allocate protected memory! mmap: %s",
strerror(errno));
ret = -1;
goto out;
}
pr_mem_next = pr_mem_base + MALLOC_MP_LIM;
pr_mem_left = pr_mem_size;
locations = strmap_new();
// change el value pointer to protected
for (el = cfg; el != NULL; el = el->next) {
if (prot_strings_helper(locations, &pr_mem_next, &pr_mem_left,
&el->param->value) < 0) {
ret = -2;
goto out;
}
if (prot_strings_helper(locations, &pr_mem_next, &pr_mem_left,
&el->param->value2) < 0) {
ret = -2;
goto out;
}
el->param->prot = 1;
}
// protecting from writes
if (mprotect(pr_mem_base, MALLOC_MP_LIM + pr_mem_size, PROT_READ)) {
log_err(LD_BUG,"(Sandbox) failed to protect memory! mprotect: %s",
strerror(errno));
ret = -3;
goto out;
}
/*
* Setting sandbox restrictions so the string memory cannot be tampered with
*/
// no mremap of the protected base address
ret = seccomp_rule_add_1(ctx, SCMP_ACT_KILL, SCMP_SYS(mremap),
SCMP_CMP(0, SCMP_CMP_EQ, (intptr_t) pr_mem_base));
if (ret) {
log_err(LD_BUG,"(Sandbox) mremap protected memory filter fail!");
goto out;
}
// no munmap of the protected base address
ret = seccomp_rule_add_1(ctx, SCMP_ACT_KILL, SCMP_SYS(munmap),
SCMP_CMP(0, SCMP_CMP_EQ, (intptr_t) pr_mem_base));
if (ret) {
log_err(LD_BUG,"(Sandbox) munmap protected memory filter fail!");
goto out;
}
/*
* Allow mprotect with PROT_READ|PROT_WRITE because openssl uses it, but
* never over the memory region used by the protected strings.
*
* PROT_READ|PROT_WRITE was originally fully allowed in sb_mprotect(), but
* had to be removed due to limitation of libseccomp regarding intervals.
*
* There is a restriction on how much you can mprotect with R|W up to the
* size of the canary.
*/
ret = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mprotect),
SCMP_CMP(0, SCMP_CMP_LT, (intptr_t) pr_mem_base),
SCMP_CMP(1, SCMP_CMP_LE, MALLOC_MP_LIM),
SCMP_CMP(2, SCMP_CMP_EQ, PROT_READ|PROT_WRITE));
if (ret) {
log_err(LD_BUG,"(Sandbox) mprotect protected memory filter fail (LT)!");
goto out;
}
ret = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mprotect),
SCMP_CMP(0, SCMP_CMP_GT, (intptr_t) pr_mem_base + pr_mem_size +
MALLOC_MP_LIM),
SCMP_CMP(1, SCMP_CMP_LE, MALLOC_MP_LIM),
SCMP_CMP(2, SCMP_CMP_EQ, PROT_READ|PROT_WRITE));
if (ret) {
log_err(LD_BUG,"(Sandbox) mprotect protected memory filter fail (GT)!");
goto out;
}
out:
strmap_free(locations, NULL);
return ret;
}
