X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=src%2Fshared%2Fcapability.c;h=58f00e6daec180c910bb72ff4cf83efd0c7c1ec3;hp=f8ee1c6838b63d00d1ad259c95b16dbd79e6e084;hb=01c94c5d0aff09b4c0e429d483c8eeba40017071;hpb=5ce70e5bcd62e89b52485961c3699312ee4a7e0e diff --git a/src/shared/capability.c b/src/shared/capability.c index f8ee1c683..58f00e6da 100644 --- a/src/shared/capability.c +++ b/src/shared/capability.c @@ -19,22 +19,18 @@ along with systemd; If not, see . ***/ -#include -#include #include #include #include -#include -#include -#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) { _cleanup_cap_free_ cap_t cap; @@ -53,11 +49,25 @@ int have_effective_cap(int value) { unsigned long cap_last_cap(void) { static thread_local unsigned long saved; static thread_local bool valid = false; - unsigned long p; + _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) { @@ -84,9 +94,9 @@ unsigned long cap_last_cap(void) { } int capability_bounding_set_drop(uint64_t drop, bool right_now) { - unsigned long i; - _cleanup_cap_free_ cap_t after_cap = NULL, temp_cap = NULL; + _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 @@ -102,6 +112,7 @@ int capability_bounding_set_drop(uint64_t drop, bool right_now) { 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); @@ -156,7 +167,8 @@ int capability_bounding_set_drop(uint64_t drop, bool right_now) { r = 0; finish: - cap_set_proc(after_cap); + if (cap_set_proc(after_cap) < 0) + return -errno; return r; } @@ -211,3 +223,85 @@ int capability_bounding_set_drop_usermode(uint64_t drop) { 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; +}