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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 13:00:47 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 13:00:47 +0000 |
commit | 2cb7e0aaedad73b076ea18c6900b0e86c5760d79 (patch) | |
tree | da68ca54bb79f4080079bf0828acda937593a4e1 /src/basic/capability-util.c | |
parent | Initial commit. (diff) | |
download | systemd-2cb7e0aaedad73b076ea18c6900b0e86c5760d79.tar.xz systemd-2cb7e0aaedad73b076ea18c6900b0e86c5760d79.zip |
Adding upstream version 247.3.upstream/247.3upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/basic/capability-util.c')
-rw-r--r-- | src/basic/capability-util.c | 605 |
1 files changed, 605 insertions, 0 deletions
diff --git a/src/basic/capability-util.c b/src/basic/capability-util.c new file mode 100644 index 0000000..c1520d9 --- /dev/null +++ b/src/basic/capability-util.c @@ -0,0 +1,605 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <errno.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/prctl.h> +#include <unistd.h> + +#include "alloc-util.h" +#include "capability-util.h" +#include "cap-list.h" +#include "fileio.h" +#include "log.h" +#include "macro.h" +#include "missing_prctl.h" +#include "parse-util.h" +#include "user-util.h" +#include "util.h" + +int have_effective_cap(int value) { + _cleanup_cap_free_ cap_t cap; + cap_flag_value_t fv; + + 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 > 63) /* 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). Let's hence protect + * ourselves against that and always cap at 63 for now. */ + p = 63; + + saved = p; + valid = true; + return p; + } + } + + /* fall back to syscall-probing for pre linux-3.2 */ + p = MIN((unsigned long) CAP_LAST_CAP, 63U); + + 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 < 63; 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_C(0xFFFFFFFF); + hi = (after >> 32) & UINT32_C(0xFFFFFFFF); + + 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[u64log2(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; +} + +int drop_capability(cap_value_t cv) { + _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, CAP_CLEAR) < 0) || + (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) || + (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0)) + return -errno; + + if (cap_set_proc(tmp_cap) < 0) + return -errno; + + return 0; +} + +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 != (uint64_t) -1; + 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 != (uint64_t) -1) { + 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 != (uint64_t) -1 || q->permitted != (uint64_t) -1 || q->effective != (uint64_t) -1) { + 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 != (uint64_t) -1) { + 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 != (uint64_t) -1) { + 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 != (uint64_t) -1) { + 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 != (uint64_t) -1) { + 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 != (uint64_t) -1) { + 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; +} |