X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=src%2Fshared%2Fcapability.c;h=dcf7ce1a69ec58b252c4dcf1bc06ace259b5c48e;hp=b2cd9ed75e8ab0d6efe9ebc1d8c7f522ae85a640;hb=51ddf61540976fc7b09ce5ace707b27f3acc3871;hpb=5430f7f2bc7330f3088b894166bf3524a067e3d8 diff --git a/src/shared/capability.c b/src/shared/capability.c index b2cd9ed75..dcf7ce1a6 100644 --- a/src/shared/capability.c +++ b/src/shared/capability.c @@ -29,37 +29,50 @@ #include #include #include +#include "grp.h" #include "macro.h" -#include "capability.h" #include "util.h" #include "log.h" +#include "fileio.h" +#include "capability.h" int have_effective_cap(int value) { - cap_t cap; + _cleanup_cap_free_ cap_t cap; cap_flag_value_t fv; - int r; - if (!(cap = cap_get_proc())) + cap = cap_get_proc(); + if (!cap) return -errno; if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0) - r = -errno; + return -errno; else - r = fv == CAP_SET; - - cap_free(cap); - return r; + return fv == CAP_SET; } unsigned long cap_last_cap(void) { - static __thread unsigned long saved; - static __thread bool valid = false; + static thread_local unsigned long saved; + static thread_local bool valid = false; + _cleanup_free_ char *content = NULL; unsigned long p; + 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) { @@ -84,3 +97,211 @@ unsigned long cap_last_cap(void) { 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); + 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[sizeof(keep_capabilities)*8]; + + for (i = 0; i < sizeof(keep_capabilities)*8; i++) + if (keep_capabilities & (1ULL << i)) + bits[j++] = i; + + 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; +}