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core: add support to specify errno in SystemCallFilter=

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This makes each system call in SystemCallFilter= blacklist optionally
takes errno name or number after a colon. The errno takes precedence
over the one given by SystemCallErrorNumber=.

C.f. #7173.
Closes #7169.
This commit is contained in:
Yu Watanabe 2017-11-11 21:35:49 +09:00
parent 473d2ec39c
commit 8cfa775f4f
7 changed files with 91 additions and 36 deletions
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7
man/systemd.exec.xml
View file

@ -1438,7 +1438,12 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
executed by the unit processes except for the listed ones will result in immediate process termination with the
<constant>SIGSYS</constant> signal (whitelisting). If the first character of the list is <literal>~</literal>,
the effect is inverted: only the listed system calls will result in immediate process termination
(blacklisting). If running in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant>
(blacklisting). Blacklisted system calls and system call groups may optionally be suffixed with a colon
(<literal>:</literal>) and <literal>errno</literal> error number (between 0 and 4095) or errno name such as
<constant>EPERM</constant>, <constant>EACCES</constant> or <constant>EUCLEAN</constant>. This value will be
returned when a blacklisted system call is triggered, instead of terminating the processes immediately.
This value takes precedence over the one given in <varname>SystemCallErrorNumber=</varname>.
If running in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant>
capability (e.g. setting <varname>User=nobody</varname>), <varname>NoNewPrivileges=yes</varname> is
implied. This feature makes use of the Secure Computing Mode 2 interfaces of the kernel ('seccomp filtering')
and is useful for enforcing a minimal sandboxing environment. Note that the <function>execve</function>,

48
src/core/dbus-execute.c
View file

@ -378,7 +378,7 @@ static int property_get_syscall_filter(
#if HAVE_SECCOMP
Iterator i;
void *id;
void *id, *val;
#endif
assert(bus);
@ -394,14 +394,33 @@ static int property_get_syscall_filter(
return r;
#if HAVE_SECCOMP
SET_FOREACH(id, c->syscall_filter, i) {
char *name;
HASHMAP_FOREACH_KEY(val, id, c->syscall_filter, i) {
_cleanup_free_ char *name = NULL;
const char *e = NULL;
char *s;
int num = PTR_TO_INT(val);
name = seccomp_syscall_resolve_num_arch(SCMP_ARCH_NATIVE, PTR_TO_INT(id) - 1);
if (!name)
continue;
r = strv_consume(&l, name);
if (num >= 0) {
e = errno_to_name(num);
if (e) {
s = strjoin(name, ":", e);
if (!s)
return -ENOMEM;
} else {
r = asprintf(&s, "%s:%d", name, num);
if (r < 0)
return -ENOMEM;
}
} else {
s = name;
name = NULL;
}
r = strv_consume(&l, s);
if (r < 0)
return r;
}
@ -1210,22 +1229,29 @@ int bus_exec_context_set_transient_property(
if (strv_length(l) == 0) {
c->syscall_whitelist = false;
c->syscall_filter = set_free(c->syscall_filter);
c->syscall_filter = hashmap_free(c->syscall_filter);
} else {
char **s;
c->syscall_whitelist = whitelist;
r = set_ensure_allocated(&c->syscall_filter, NULL);
r = hashmap_ensure_allocated(&c->syscall_filter, NULL);
if (r < 0)
return r;
STRV_FOREACH(s, l) {
if (**s == '@') {
_cleanup_free_ char *n = NULL;
int e;
r = parse_syscall_and_errno(*s, &n, &e);
if (r < 0)
return r;
if (*n == '@') {
const SyscallFilterSet *set;
const char *i;
set = syscall_filter_set_find(*s);
set = syscall_filter_set_find(n);
if (!set)
return -EINVAL;
@ -1236,7 +1262,7 @@ int bus_exec_context_set_transient_property(
if (id == __NR_SCMP_ERROR)
return -EINVAL;
r = set_put(c->syscall_filter, INT_TO_PTR(id + 1));
r = hashmap_put(c->syscall_filter, INT_TO_PTR(id + 1), INT_TO_PTR(e));
if (r < 0)
return r;
}
@ -1244,11 +1270,11 @@ int bus_exec_context_set_transient_property(
} else {
int id;
id = seccomp_syscall_resolve_name(*s);
id = seccomp_syscall_resolve_name(n);
if (id == __NR_SCMP_ERROR)
return -EINVAL;
r = set_put(c->syscall_filter, INT_TO_PTR(id + 1));
r = hashmap_put(c->syscall_filter, INT_TO_PTR(id + 1), INT_TO_PTR(e));
if (r < 0)
return r;
}

18
src/core/execute.c
View file

@ -1290,7 +1290,7 @@ static bool context_has_syscall_filters(const ExecContext *c) {
assert(c);
return c->syscall_whitelist ||
!set_isempty(c->syscall_filter);
!hashmap_isempty(c->syscall_filter);
}
static bool context_has_no_new_privileges(const ExecContext *c) {
@ -3528,7 +3528,7 @@ void exec_context_done(ExecContext *c) {
c->apparmor_profile = mfree(c->apparmor_profile);
c->smack_process_label = mfree(c->smack_process_label);
c->syscall_filter = set_free(c->syscall_filter);
c->syscall_filter = hashmap_free(c->syscall_filter);
c->syscall_archs = set_free(c->syscall_archs);
c->address_families = set_free(c->address_families);
@ -4065,7 +4065,7 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
if (c->syscall_filter) {
#if HAVE_SECCOMP
Iterator j;
void *id;
void *id, *val;
bool first = true;
#endif
@ -4077,8 +4077,10 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
fputc('~', f);
#if HAVE_SECCOMP
SET_FOREACH(id, c->syscall_filter, j) {
HASHMAP_FOREACH_KEY(val, id, c->syscall_filter, j) {
_cleanup_free_ char *name = NULL;
const char *errno_name = NULL;
int num = PTR_TO_INT(val);
if (first)
first = false;
@ -4087,6 +4089,14 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
name = seccomp_syscall_resolve_num_arch(SCMP_ARCH_NATIVE, PTR_TO_INT(id) - 1);
fputs(strna(name), f);
if (num >= 0) {
errno_name = errno_to_name(num);
if (errno_name)
fprintf(f, ":%s", errno_name);
else
fprintf(f, ":%d", num);
}
}
#endif

2
src/core/execute.h
View file

@ -242,7 +242,7 @@ struct ExecContext {
unsigned long restrict_namespaces; /* The CLONE_NEWxyz flags permitted to the unit's processes */
Set *syscall_filter;
Hashmap *syscall_filter;
Set *syscall_archs;
int syscall_errno;
bool syscall_whitelist:1;

26
src/core/load-fragment.c
View file

@ -2632,7 +2632,8 @@ static int syscall_filter_parse_one(
ExecContext *c,
bool invert,
const char *t,
bool warn) {
bool warn,
int errno_num) {
int r;
if (t[0] == '@') {
@ -2647,7 +2648,7 @@ static int syscall_filter_parse_one(
}
NULSTR_FOREACH(i, set->value) {
r = syscall_filter_parse_one(unit, filename, line, c, invert, i, false);
r = syscall_filter_parse_one(unit, filename, line, c, invert, i, false, errno_num);
if (r < 0)
return r;
}
@ -2665,13 +2666,13 @@ static int syscall_filter_parse_one(
* we want to allow it, then remove it from the list
*/
if (!invert == c->syscall_whitelist) {
r = set_put(c->syscall_filter, INT_TO_PTR(id + 1));
r = hashmap_put(c->syscall_filter, INT_TO_PTR(id + 1), INT_TO_PTR(errno_num));
if (r == 0)
return 0;
if (r < 0)
return log_oom();
} else
(void) set_remove(c->syscall_filter, INT_TO_PTR(id + 1));
(void) hashmap_remove(c->syscall_filter, INT_TO_PTR(id + 1));
}
return 0;
@ -2702,7 +2703,7 @@ int config_parse_syscall_filter(
if (isempty(rvalue)) {
/* Empty assignment resets the list */
c->syscall_filter = set_free(c->syscall_filter);
c->syscall_filter = hashmap_free(c->syscall_filter);
c->syscall_whitelist = false;
return 0;
}
@ -2713,7 +2714,7 @@ int config_parse_syscall_filter(
}
if (!c->syscall_filter) {
c->syscall_filter = set_new(NULL);
c->syscall_filter = hashmap_new(NULL);
if (!c->syscall_filter)
return log_oom();
@ -2725,7 +2726,7 @@ int config_parse_syscall_filter(
c->syscall_whitelist = true;
/* Accept default syscalls if we are on a whitelist */
r = syscall_filter_parse_one(unit, filename, line, c, false, "@default", false);
r = syscall_filter_parse_one(unit, filename, line, c, false, "@default", false, -1);
if (r < 0)
return r;
}
@ -2733,7 +2734,8 @@ int config_parse_syscall_filter(
p = rvalue;
for (;;) {
_cleanup_free_ char *word = NULL;
_cleanup_free_ char *word = NULL, *name = NULL;
int num;
r = extract_first_word(&p, &word, NULL, 0);
if (r == 0)
@ -2745,7 +2747,13 @@ int config_parse_syscall_filter(
break;
}
r = syscall_filter_parse_one(unit, filename, line, c, invert, word, true);
r = parse_syscall_and_errno(word, &name, &num);
if (r < 0) {
log_syntax(unit, LOG_WARNING, filename, line, r, "Failed to parse syscall:errno, ignoring: %s", word);
continue;
}
r = syscall_filter_parse_one(unit, filename, line, c, invert, name, true, num);
if (r < 0)
return r;
}

22
src/shared/seccomp-util.c
View file

@ -900,20 +900,20 @@ int seccomp_load_syscall_filter_set(uint32_t default_action, const SyscallFilter
return 0;
}
int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Set* set, uint32_t action) {
int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Hashmap* set, uint32_t action) {
uint32_t arch;
int r;
/* Similar to seccomp_load_syscall_filter_set(), but takes a raw Set* of syscalls, instead of a
* SyscallFilterSet* table. */
if (set_isempty(set) && default_action == SCMP_ACT_ALLOW)
if (hashmap_isempty(set) && default_action == SCMP_ACT_ALLOW)
return 0;
SECCOMP_FOREACH_LOCAL_ARCH(arch) {
_cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
Iterator i;
void *id;
void *id, *val;
log_debug("Operating on architecture: %s", seccomp_arch_to_string(arch));
@ -921,8 +921,14 @@ int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Set* set, uint3
if (r < 0)
return r;
SET_FOREACH(id, set, i) {
r = seccomp_rule_add_exact(seccomp, action, PTR_TO_INT(id) - 1, 0);
HASHMAP_FOREACH_KEY(val, id, set, i) {
uint32_t a = action;
int e = PTR_TO_INT(val);
if (action != SCMP_ACT_ALLOW && e >= 0)
a = SCMP_ACT_ERRNO(e);
r = seccomp_rule_add_exact(seccomp, a, PTR_TO_INT(id) - 1, 0);
if (r < 0) {
/* If the system call is not known on this architecture, then that's fine, let's ignore it */
_cleanup_free_ char *n = NULL;
@ -1515,7 +1521,7 @@ int parse_syscall_archs(char **l, Set **archs) {
return 0;
}
int seccomp_filter_set_add(Set *filter, bool add, const SyscallFilterSet *set) {
int seccomp_filter_set_add(Hashmap *filter, bool add, const SyscallFilterSet *set) {
const char *i;
int r;
@ -1543,11 +1549,11 @@ int seccomp_filter_set_add(Set *filter, bool add, const SyscallFilterSet *set) {
}
if (add) {
r = set_put(filter, INT_TO_PTR(id + 1));
r = hashmap_put(filter, INT_TO_PTR(id + 1), INT_TO_PTR(-1));
if (r < 0)
return r;
} else
(void) set_remove(filter, INT_TO_PTR(id + 1));
(void) hashmap_remove(filter, INT_TO_PTR(id + 1));
}
}

4
src/shared/seccomp-util.h
View file

@ -73,12 +73,12 @@ extern const SyscallFilterSet syscall_filter_sets[];
const SyscallFilterSet *syscall_filter_set_find(const char *name);
int seccomp_filter_set_add(Set *s, bool b, const SyscallFilterSet *set);
int seccomp_filter_set_add(Hashmap *s, bool b, const SyscallFilterSet *set);
int seccomp_add_syscall_filter_item(scmp_filter_ctx *ctx, const char *name, uint32_t action, char **exclude);
int seccomp_load_syscall_filter_set(uint32_t default_action, const SyscallFilterSet *set, uint32_t action);
int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Set* set, uint32_t action);
int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Hashmap* set, uint32_t action);
int seccomp_restrict_archs(Set *archs);
int seccomp_restrict_namespaces(unsigned long retain);