| /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ |
| |
| /*** |
| 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 <unistd.h> |
| #include <errno.h> |
| #include <stdio.h> |
| #include <sys/capability.h> |
| #include <sys/prctl.h> |
| #include "grp.h" |
| |
| #include "macro.h" |
| #include "util.h" |
| #include "log.h" |
| #include "fileio.h" |
| #include "capability.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_bounding_set_drop(uint64_t drop, 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 (drop & ((uint64_t) 1ULL << (uint64_t) 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 drop) { |
| 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 & ~drop; |
| |
| 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 drop) { |
| int r; |
| |
| r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop); |
| if (r < 0) |
| return r; |
| |
| r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop); |
| 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"); |
| |
| if (setgroups(0, NULL) < 0) |
| return log_error_errno(errno, "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) { |
| log_error_errno(errno, "Failed to enable capabilities bits: %m"); |
| return -errno; |
| } |
| |
| 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; |
| } |