diff options
Diffstat (limited to 'src/libsystemd-basic/src/capability-util.c')
| -rw-r--r-- | src/libsystemd-basic/src/capability-util.c | 363 |
1 files changed, 363 insertions, 0 deletions
diff --git a/src/libsystemd-basic/src/capability-util.c b/src/libsystemd-basic/src/capability-util.c new file mode 100644 index 0000000000..9f104b0ba1 --- /dev/null +++ b/src/libsystemd-basic/src/capability-util.c @@ -0,0 +1,363 @@ +/*** + This file is part of systemd. + + Copyright 2010 Lennart Poettering + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +#include <errno.h> +#include <grp.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/capability.h> +#include <sys/prctl.h> +#include <unistd.h> + +#include "systemd-basic/alloc-util.h" +#include "systemd-basic/capability-util.h" +#include "systemd-basic/fileio.h" +#include "systemd-basic/log.h" +#include "systemd-basic/macro.h" +#include "systemd-basic/parse-util.h" +#include "systemd-basic/user-util.h" +#include "systemd-basic/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; + else + return fv == CAP_SET; +} + +unsigned long cap_last_cap(void) { + static thread_local unsigned long 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) { + saved = p; + valid = true; + return p; + } + } + + /* fall back to syscall-probing for pre linux-3.2 */ + p = (unsigned long) CAP_LAST_CAP; + + 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++) + 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) { + unsigned long i; + + /* Add capabilities in the set to the inherited caps. Do not apply + * them yet. */ + + for (i = 0; i < cap_last_cap(); i++) { + + if (set & (UINT64_C(1) << i)) { + cap_value_t v; + + v = (cap_value_t) i; + + /* Make the capability inheritable. */ + if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0) + return -errno; + } + } + + return 0; +} + +int capability_ambient_set_apply(uint64_t set, bool also_inherit) { + unsigned long i; + _cleanup_cap_free_ cap_t caps = NULL; + + /* Add the capabilities to the ambient set. */ + + if (also_inherit) { + int r; + 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 (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; + } + } + + return 0; +} + +int capability_bounding_set_drop(uint64_t keep, bool right_now) { + _cleanup_cap_free_ cap_t after_cap = NULL; + cap_flag_value_t fv; + unsigned long i; + 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. */ + + after_cap = cap_get_proc(); + if (!after_cap) + return -errno; + + if (cap_get_flag(after_cap, 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(after_cap); + if (!temp_cap) { + r = -errno; + goto finish; + } + + if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) { + r = -errno; + goto finish; + } + + if (cap_set_proc(temp_cap) < 0) { + r = -errno; + goto finish; + } + } + + for (i = 0; i <= cap_last_cap(); i++) { + + if (!(keep & (UINT64_C(1) << i))) { + cap_value_t v; + + /* Drop it from the bounding set */ + if (prctl(PR_CAPBSET_DROP, i) < 0) { + r = -errno; + 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) + return -errno; + + return r; +} + +static int drop_from_file(const char *fn, uint64_t keep) { + int r, k; + uint32_t hi, lo; + uint64_t current, after; + char *p; + + r = read_one_line_file(fn, &p); + if (r < 0) + return r; + + assert_cc(sizeof(hi) == sizeof(unsigned)); + assert_cc(sizeof(lo) == sizeof(unsigned)); + + k = sscanf(p, "%u %u", &lo, &hi); + free(p); + + if (k != 2) + return -EIO; + + current = (uint64_t) lo | ((uint64_t) hi << 32ULL); + after = current & keep; + + if (current == after) + return 0; + + lo = (unsigned) (after & 0xFFFFFFFFULL); + hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL); + + if (asprintf(&p, "%u %u", lo, hi) < 0) + return -ENOMEM; + + r = write_string_file(fn, p, WRITE_STRING_FILE_CREATE); + free(p); + + return r; +} + +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) { + _cleanup_cap_free_ cap_t d = NULL; + unsigned i, j = 0; + 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() */ + if (prctl(PR_SET_KEEPCAPS, 1) < 0) + return log_error_errno(errno, "Failed to enable keep capabilities flag: %m"); + + r = setresuid(uid, uid, uid); + if (r < 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, except the ones we want */ + 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 */ + d = cap_init(); + if (!d) + return log_oom(); + + if (keep_capabilities) { + cap_value_t bits[u64log2(keep_capabilities) + 1]; + + 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 & (1ULL << (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; +} |