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Merge pull request #30305 from yuwata/seccomp-fix

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seccomp: override the default action only when the filter is allow-list
This commit is contained in:
Yu Watanabe 2023-12-04 11:44:58 +09:00 committed by GitHub
commit b88f0fdc87
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1 changed files with 65 additions and 20 deletions
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59
src/shared/seccomp-util.c
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@ -1080,8 +1080,24 @@ static int add_syscall_filter_set(
return 0;
}
static uint32_t override_default_action(uint32_t default_action) {
/* When the requested filter is an allow-list, and the default action is something critical, we
* install ENOSYS as the default action, but it will only apply to syscalls which are not in the
* @known set. */
if (default_action == SCMP_ACT_ALLOW)
return default_action;
#ifdef SCMP_ACT_LOG
if (default_action == SCMP_ACT_LOG)
return default_action;
#endif
return SCMP_ACT_ERRNO(ENOSYS);
}
int seccomp_load_syscall_filter_set(uint32_t default_action, const SyscallFilterSet *set, uint32_t action, bool log_missing) {
uint32_t arch;
uint32_t arch, default_action_override;
int r;
assert(set);
@ -1089,19 +1105,47 @@ int seccomp_load_syscall_filter_set(uint32_t default_action, const SyscallFilter
/* The one-stop solution: allocate a seccomp object, add the specified filter to it, and apply it. Once for
* each local arch. */
default_action_override = override_default_action(default_action);
SECCOMP_FOREACH_LOCAL_ARCH(arch) {
_cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
_cleanup_strv_free_ char **added = NULL;
log_trace("Operating on architecture: %s", seccomp_arch_to_string(arch));
r = seccomp_init_for_arch(&seccomp, arch, default_action);
r = seccomp_init_for_arch(&seccomp, arch, default_action_override);
if (r < 0)
return r;
r = add_syscall_filter_set(seccomp, set, action, NULL, log_missing, NULL);
r = add_syscall_filter_set(seccomp, set, action, NULL, log_missing, &added);
if (r < 0)
return log_debug_errno(r, "Failed to add filter set: %m");
if (default_action != default_action_override)
NULSTR_FOREACH(name, syscall_filter_sets[SYSCALL_FILTER_SET_KNOWN].value) {
int id;
id = seccomp_syscall_resolve_name(name);
if (id < 0)
continue;
/* Ignore the syscall if it was already handled above */
if (strv_contains(added, name))
continue;
r = seccomp_rule_add_exact(seccomp, default_action, id, 0);
if (r < 0 && r != -EDOM) /* EDOM means that the syscall is not available for arch */
return log_debug_errno(r, "Failed to add rule for system call %s() / %d: %m",
name, id);
}
#if (SCMP_VER_MAJOR == 2 && SCMP_VER_MINOR >= 5) || SCMP_VER_MAJOR > 2
/* We have a large filter here, so let's turn on the binary tree mode if possible. */
r = seccomp_attr_set(seccomp, SCMP_FLTATR_CTL_OPTIMIZE, 2);
if (r < 0)
log_warning_errno(r, "Failed to set SCMP_FLTATR_CTL_OPTIMIZE, ignoring: %m");
#endif
r = seccomp_load(seccomp);
if (ERRNO_IS_NEG_SECCOMP_FATAL(r))
return r;
@ -1114,7 +1158,7 @@ int seccomp_load_syscall_filter_set(uint32_t default_action, const SyscallFilter
}
int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Hashmap* filter, uint32_t action, bool log_missing) {
uint32_t arch;
uint32_t arch, default_action_override;
int r;
/* Similar to seccomp_load_syscall_filter_set(), but takes a raw Hashmap* of syscalls, instead
@ -1123,15 +1167,15 @@ int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Hashmap* filter
if (hashmap_isempty(filter) && default_action == SCMP_ACT_ALLOW)
return 0;
default_action_override = override_default_action(default_action);
SECCOMP_FOREACH_LOCAL_ARCH(arch) {
_cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
void *syscall_id, *val;
log_trace("Operating on architecture: %s", seccomp_arch_to_string(arch));
/* We install ENOSYS as the default action, but it will only apply to syscalls which are not
* in the @known set. */
r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ERRNO(ENOSYS));
r = seccomp_init_for_arch(&seccomp, arch, default_action_override);
if (r < 0)
return r;
@ -1166,6 +1210,7 @@ int seccomp_load_syscall_filter_set_raw(uint32_t default_action, Hashmap* filter
}
}
if (default_action != default_action_override)
NULSTR_FOREACH(name, syscall_filter_sets[SYSCALL_FILTER_SET_KNOWN].value) {
int id;