}
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
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");
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];
- unsigned i, j = 0;
+ cap_value_t bits[u64log2(keep_capabilities) + 1];
- for (i = 0; i < sizeof(keep_capabilities)*8; i++)
+ 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");
+ if (cap_set_proc(d) < 0)
+ return log_error_errno(errno, "Failed to increase capabilities: %m");
+ }
return 0;
}