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6159386)
From fd.o bug 88898:
systemd-resolved fails to start:
Failed to drop capabilities: Operation not permitted
Broken in
f11943c53ec181829a821c6b27acf828bab71caa.
Drop all capabilities:
1. prctl(PR_SET_KEEPCAPS, keep_capabilities != 0) // 0 when we drop all
capabilities
2. setresuid() // bye bye capabilities
3. Add CAP_SETPCAP // fails because we have no capabilities
4. Reduce capability bounding set
5. Drop capabilities
6. prctl(PR_SET_KEEPCAPS, 0)
Capabilites should always be kept after setresuid() so that the capability
bounding set can be reduced.
Based-on-a-patch-by: mustrumr97@gmail.com
https://bugs.freedesktop.org/show_bug.cgi?id=88898
We must be careful not to leave PR_SET_KEEPCAPS on. We could use the
setresuid() call to drop capabilities, but the rules when capabilities
are dropped are fairly complex, since a transition to non-zero uid must
happen. Let's instead keep the capabilities during setresuid(), and drop
them later.
}
int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
}
int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
- cap_value_t bits[sizeof(keep_capabilities)*8];
_cleanup_cap_free_ cap_t d = NULL;
unsigned i, j = 0;
int r;
_cleanup_cap_free_ cap_t d = NULL;
unsigned i, j = 0;
int r;
if (setgroups(0, NULL) < 0)
return log_error_errno(errno, "Failed to drop auxiliary groups list: %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 we need them */
- if (prctl(PR_SET_KEEPCAPS, keep_capabilities != 0) < 0)
+ /* 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);
return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
r = setresuid(uid, uid, uid);
if (r < 0)
return log_error_errno(r, "Failed to drop capabilities: %m");
if (r < 0)
return log_error_errno(r, "Failed to drop capabilities: %m");
- if (keep_capabilities == 0) /* All is gone, we can exit early */
- return 0;
-
/* Now upgrade the permitted caps we still kept to effective caps */
d = cap_init();
if (!d)
return log_oom();
/* Now upgrade the permitted caps we still kept to effective caps */
d = cap_init();
if (!d)
return log_oom();
- for (i = 0; i < sizeof(keep_capabilities)*8; i++)
- if (keep_capabilities & (1ULL << i))
- bits[j++] = i;
+ if (keep_capabilities) {
+ cap_value_t bits[sizeof(keep_capabilities)*8];
- 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;
- }
+ for (i = 0; i < sizeof(keep_capabilities)*8; i++)
+ if (keep_capabilities & (1ULL << i))
+ bits[j++] = i;
- if (cap_set_proc(d) < 0)
- return log_error_errno(errno, "Failed to increase capabilities: %m");
+ 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");
+ }