/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #include #include #include "alloc-util.h" #include "capability-util.h" #include "cap-list.h" #include "fileio.h" #include "log.h" #include "logarithm.h" #include "macro.h" #include "missing_prctl.h" #include "missing_threads.h" #include "parse-util.h" #include "user-util.h" int have_effective_cap(int value) { _cleanup_cap_free_ cap_t cap = NULL; cap_flag_value_t fv = CAP_CLEAR; /* To avoid false-positive use-of-uninitialized-value error reported * by fuzzers. */ cap = cap_get_proc(); if (!cap) return -errno; if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0) return -errno; return fv == CAP_SET; } unsigned cap_last_cap(void) { static thread_local unsigned saved; static thread_local bool valid = false; _cleanup_free_ char *content = NULL; unsigned long p = 0; int r; if (valid) return saved; /* available since linux-3.2 */ r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content); if (r >= 0) { r = safe_atolu(content, &p); if (r >= 0) { if (p > CAP_LIMIT) /* Safety for the future: if one day the kernel learns more than * 64 caps, then we are in trouble (since we, as much userspace * and kernel space store capability masks in uint64_t types). We * also want to use UINT64_MAX as marker for "unset". Hence let's * hence protect ourselves against that and always cap at 62 for * now. */ p = CAP_LIMIT; saved = p; valid = true; return p; } } /* fall back to syscall-probing for pre linux-3.2 */ p = (unsigned long) MIN(CAP_LAST_CAP, CAP_LIMIT); if (prctl(PR_CAPBSET_READ, p) < 0) { /* Hmm, look downwards, until we find one that works */ for (p--; p > 0; p--) if (prctl(PR_CAPBSET_READ, p) >= 0) break; } else { /* Hmm, look upwards, until we find one that doesn't work */ for (; p < CAP_LIMIT; p++) if (prctl(PR_CAPBSET_READ, p+1) < 0) break; } saved = p; valid = true; return p; } int capability_update_inherited_set(cap_t caps, uint64_t set) { /* Add capabilities in the set to the inherited caps, drops capabilities not in the set. * Do not apply them yet. */ for (unsigned i = 0; i <= cap_last_cap(); i++) { cap_flag_value_t flag = set & (UINT64_C(1) << i) ? CAP_SET : CAP_CLEAR; cap_value_t v; v = (cap_value_t) i; if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, flag) < 0) return -errno; } return 0; } int capability_ambient_set_apply(uint64_t set, bool also_inherit) { _cleanup_cap_free_ cap_t caps = NULL; int r; /* Remove capabilities requested in ambient set, but not in the bounding set */ for (unsigned i = 0; i <= cap_last_cap(); i++) { if (set == 0) break; if (FLAGS_SET(set, (UINT64_C(1) << i)) && prctl(PR_CAPBSET_READ, i) != 1) { log_debug("Ambient capability %s requested but missing from bounding set," " suppressing automatically.", capability_to_name(i)); set &= ~(UINT64_C(1) << i); } } /* Add the capabilities to the ambient set (an possibly also the inheritable set) */ /* Check that we can use PR_CAP_AMBIENT or quit early. */ if (!ambient_capabilities_supported()) return (set & all_capabilities()) == 0 ? 0 : -EOPNOTSUPP; /* if actually no ambient caps are to be set, be silent, * otherwise fail recognizably */ if (also_inherit) { caps = cap_get_proc(); if (!caps) return -errno; r = capability_update_inherited_set(caps, set); if (r < 0) return -errno; if (cap_set_proc(caps) < 0) return -errno; } for (unsigned i = 0; i <= cap_last_cap(); i++) { if (set & (UINT64_C(1) << i)) { /* Add the capability to the ambient set. */ if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0) return -errno; } else { /* Drop the capability so we don't inherit capabilities we didn't ask for. */ r = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, i, 0, 0); if (r < 0) return -errno; if (r) if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_LOWER, i, 0, 0) < 0) return -errno; } } return 0; } int capability_gain_cap_setpcap(cap_t *ret_before_caps) { _cleanup_cap_free_ cap_t caps = NULL; cap_flag_value_t fv; caps = cap_get_proc(); if (!caps) return -errno; if (cap_get_flag(caps, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0) return -errno; if (fv != CAP_SET) { _cleanup_cap_free_ cap_t temp_cap = NULL; static const cap_value_t v = CAP_SETPCAP; temp_cap = cap_dup(caps); if (!temp_cap) return -errno; if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) return -errno; if (cap_set_proc(temp_cap) < 0) log_debug_errno(errno, "Can't acquire effective CAP_SETPCAP bit, ignoring: %m"); /* If we didn't manage to acquire the CAP_SETPCAP bit, we continue anyway, after all this just means * we'll fail later, when we actually intend to drop some capabilities or try to set securebits. */ } if (ret_before_caps) /* Return the capabilities as they have been before setting CAP_SETPCAP */ *ret_before_caps = TAKE_PTR(caps); return 0; } int capability_bounding_set_drop(uint64_t keep, bool right_now) { _cleanup_cap_free_ cap_t before_cap = NULL, after_cap = NULL; int r; /* If we are run as PID 1 we will lack CAP_SETPCAP by default * in the effective set (yes, the kernel drops that when * executing init!), so get it back temporarily so that we can * call PR_CAPBSET_DROP. */ r = capability_gain_cap_setpcap(&before_cap); if (r < 0) return r; after_cap = cap_dup(before_cap); if (!after_cap) return -errno; for (unsigned i = 0; i <= cap_last_cap(); i++) { cap_value_t v; if ((keep & (UINT64_C(1) << i))) continue; /* Drop it from the bounding set */ if (prctl(PR_CAPBSET_DROP, i) < 0) { r = -errno; /* If dropping the capability failed, let's see if we didn't have it in the first place. If so, * continue anyway, as dropping a capability we didn't have in the first place doesn't really * matter anyway. */ if (prctl(PR_CAPBSET_READ, i) != 0) goto finish; } v = (cap_value_t) i; /* Also drop it from the inheritable set, so * that anything we exec() loses the * capability for good. */ if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) { r = -errno; goto finish; } /* If we shall apply this right now drop it * also from our own capability sets. */ if (right_now) { if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 || cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) { r = -errno; goto finish; } } } r = 0; finish: if (cap_set_proc(after_cap) < 0) { /* If there are no actual changes anyway then let's ignore this error. */ if (cap_compare(before_cap, after_cap) != 0) r = -errno; } return r; } static int drop_from_file(const char *fn, uint64_t keep) { _cleanup_free_ char *p = NULL; uint64_t current, after; uint32_t hi, lo; int r, k; r = read_one_line_file(fn, &p); if (r < 0) return r; k = sscanf(p, "%" PRIu32 " %" PRIu32, &lo, &hi); if (k != 2) return -EIO; current = (uint64_t) lo | ((uint64_t) hi << 32); after = current & keep; if (current == after) return 0; lo = after & UINT32_MAX; hi = (after >> 32) & UINT32_MAX; return write_string_filef(fn, 0, "%" PRIu32 " %" PRIu32, lo, hi); } int capability_bounding_set_drop_usermode(uint64_t keep) { int r; r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep); if (r < 0) return r; r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep); if (r < 0) return r; return r; } int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) { int r; /* Unfortunately we cannot leave privilege dropping to PID 1 here, since we want to run as user but * want to keep some capabilities. Since file capabilities have been introduced this cannot be done * across exec() anymore, unless our binary has the capability configured in the file system, which * we want to avoid. */ if (setresgid(gid, gid, gid) < 0) return log_error_errno(errno, "Failed to change group ID: %m"); r = maybe_setgroups(0, NULL); if (r < 0) return log_error_errno(r, "Failed to drop auxiliary groups list: %m"); /* Ensure we keep the permitted caps across the setresuid(). Note that we do this even if we actually * don't want to keep any capabilities, since we want to be able to drop them from the bounding set * too, and we can only do that if we have capabilities. */ if (prctl(PR_SET_KEEPCAPS, 1) < 0) return log_error_errno(errno, "Failed to enable keep capabilities flag: %m"); if (setresuid(uid, uid, uid) < 0) return log_error_errno(errno, "Failed to change user ID: %m"); if (prctl(PR_SET_KEEPCAPS, 0) < 0) return log_error_errno(errno, "Failed to disable keep capabilities flag: %m"); /* Drop all caps from the bounding set (as well as the inheritable/permitted/effective sets), except * the ones we want to keep */ r = capability_bounding_set_drop(keep_capabilities, true); if (r < 0) return log_error_errno(r, "Failed to drop capabilities: %m"); /* Now upgrade the permitted caps we still kept to effective caps */ if (keep_capabilities != 0) { cap_value_t bits[log2u64(keep_capabilities) + 1]; _cleanup_cap_free_ cap_t d = NULL; unsigned i, j = 0; d = cap_init(); if (!d) return log_oom(); for (i = 0; i < ELEMENTSOF(bits); i++) if (keep_capabilities & (1ULL << i)) bits[j++] = i; /* use enough bits */ assert(i == 64 || (keep_capabilities >> i) == 0); /* don't use too many bits */ assert(keep_capabilities & (UINT64_C(1) << (i - 1))); if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 || cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) return log_error_errno(errno, "Failed to enable capabilities bits: %m"); if (cap_set_proc(d) < 0) return log_error_errno(errno, "Failed to increase capabilities: %m"); } return 0; } static int change_capability(cap_value_t cv, cap_flag_value_t flag) { _cleanup_cap_free_ cap_t tmp_cap = NULL; tmp_cap = cap_get_proc(); if (!tmp_cap) return -errno; if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, flag) < 0) || (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, flag) < 0) || (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, flag) < 0)) return -errno; if (cap_set_proc(tmp_cap) < 0) return -errno; return 0; } int drop_capability(cap_value_t cv) { return change_capability(cv, CAP_CLEAR); } int keep_capability(cap_value_t cv) { return change_capability(cv, CAP_SET); } bool ambient_capabilities_supported(void) { static int cache = -1; if (cache >= 0) return cache; /* If PR_CAP_AMBIENT returns something valid, or an unexpected error code we assume that ambient caps are * available. */ cache = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_KILL, 0, 0) >= 0 || !IN_SET(errno, EINVAL, EOPNOTSUPP, ENOSYS); return cache; } bool capability_quintet_mangle(CapabilityQuintet *q) { uint64_t combined, drop = 0; bool ambient_supported; assert(q); combined = q->effective | q->bounding | q->inheritable | q->permitted; ambient_supported = q->ambient != CAP_MASK_UNSET; if (ambient_supported) combined |= q->ambient; for (unsigned i = 0; i <= cap_last_cap(); i++) { unsigned long bit = UINT64_C(1) << i; if (!FLAGS_SET(combined, bit)) continue; if (prctl(PR_CAPBSET_READ, i) > 0) continue; drop |= bit; log_debug("Not in the current bounding set: %s", capability_to_name(i)); } q->effective &= ~drop; q->bounding &= ~drop; q->inheritable &= ~drop; q->permitted &= ~drop; if (ambient_supported) q->ambient &= ~drop; return drop != 0; /* Let the caller know we changed something */ } int capability_quintet_enforce(const CapabilityQuintet *q) { _cleanup_cap_free_ cap_t c = NULL, modified = NULL; int r; if (q->ambient != CAP_MASK_UNSET) { bool changed = false; c = cap_get_proc(); if (!c) return -errno; /* In order to raise the ambient caps set we first need to raise the matching * inheritable + permitted cap */ for (unsigned i = 0; i <= cap_last_cap(); i++) { uint64_t m = UINT64_C(1) << i; cap_value_t cv = (cap_value_t) i; cap_flag_value_t old_value_inheritable, old_value_permitted; if ((q->ambient & m) == 0) continue; if (cap_get_flag(c, cv, CAP_INHERITABLE, &old_value_inheritable) < 0) return -errno; if (cap_get_flag(c, cv, CAP_PERMITTED, &old_value_permitted) < 0) return -errno; if (old_value_inheritable == CAP_SET && old_value_permitted == CAP_SET) continue; if (cap_set_flag(c, CAP_INHERITABLE, 1, &cv, CAP_SET) < 0) return -errno; if (cap_set_flag(c, CAP_PERMITTED, 1, &cv, CAP_SET) < 0) return -errno; changed = true; } if (changed) if (cap_set_proc(c) < 0) return -errno; r = capability_ambient_set_apply(q->ambient, false); if (r < 0) return r; } if (q->inheritable != CAP_MASK_UNSET || q->permitted != CAP_MASK_UNSET || q->effective != CAP_MASK_UNSET) { bool changed = false; if (!c) { c = cap_get_proc(); if (!c) return -errno; } for (unsigned i = 0; i <= cap_last_cap(); i++) { uint64_t m = UINT64_C(1) << i; cap_value_t cv = (cap_value_t) i; if (q->inheritable != CAP_MASK_UNSET) { cap_flag_value_t old_value, new_value; if (cap_get_flag(c, cv, CAP_INHERITABLE, &old_value) < 0) { if (errno == EINVAL) /* If the kernel knows more caps than this * version of libcap, then this will return * EINVAL. In that case, simply ignore it, * pretend it doesn't exist. */ continue; return -errno; } new_value = (q->inheritable & m) ? CAP_SET : CAP_CLEAR; if (old_value != new_value) { changed = true; if (cap_set_flag(c, CAP_INHERITABLE, 1, &cv, new_value) < 0) return -errno; } } if (q->permitted != CAP_MASK_UNSET) { cap_flag_value_t old_value, new_value; if (cap_get_flag(c, cv, CAP_PERMITTED, &old_value) < 0) { if (errno == EINVAL) continue; return -errno; } new_value = (q->permitted & m) ? CAP_SET : CAP_CLEAR; if (old_value != new_value) { changed = true; if (cap_set_flag(c, CAP_PERMITTED, 1, &cv, new_value) < 0) return -errno; } } if (q->effective != CAP_MASK_UNSET) { cap_flag_value_t old_value, new_value; if (cap_get_flag(c, cv, CAP_EFFECTIVE, &old_value) < 0) { if (errno == EINVAL) continue; return -errno; } new_value = (q->effective & m) ? CAP_SET : CAP_CLEAR; if (old_value != new_value) { changed = true; if (cap_set_flag(c, CAP_EFFECTIVE, 1, &cv, new_value) < 0) return -errno; } } } if (changed) { /* In order to change the bounding caps, we need to keep CAP_SETPCAP for a bit * longer. Let's add it to our list hence for now. */ if (q->bounding != CAP_MASK_UNSET) { cap_value_t cv = CAP_SETPCAP; modified = cap_dup(c); if (!modified) return -ENOMEM; if (cap_set_flag(modified, CAP_PERMITTED, 1, &cv, CAP_SET) < 0) return -errno; if (cap_set_flag(modified, CAP_EFFECTIVE, 1, &cv, CAP_SET) < 0) return -errno; if (cap_compare(modified, c) == 0) { /* No change? then drop this nonsense again */ cap_free(modified); modified = NULL; } } /* Now, let's enforce the caps for the first time. Note that this is where we acquire * caps in any of the sets we currently don't have. We have to do this before * dropping the bounding caps below, since at that point we can never acquire new * caps in inherited/permitted/effective anymore, but only lose them. */ if (cap_set_proc(modified ?: c) < 0) return -errno; } } if (q->bounding != CAP_MASK_UNSET) { r = capability_bounding_set_drop(q->bounding, false); if (r < 0) return r; } /* If needed, let's now set the caps again, this time in the final version, which differs from what * we have already set only in the CAP_SETPCAP bit, which we needed for dropping the bounding * bits. This call only undoes bits and doesn't acquire any which means the bounding caps don't * matter. */ if (modified) if (cap_set_proc(c) < 0) return -errno; return 0; } int capability_get_ambient(uint64_t *ret) { uint64_t a = 0; int r; assert(ret); if (!ambient_capabilities_supported()) { *ret = 0; return 0; } for (unsigned i = 0; i <= cap_last_cap(); i++) { r = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, i, 0, 0); if (r < 0) return -errno; if (r) a |= UINT64_C(1) << i; } *ret = a; return 1; }