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authorZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2015-02-01 14:33:10 -0500
committerZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2015-02-01 17:22:32 -0500
commit51ddf61540976fc7b09ce5ace707b27f3acc3871 (patch)
treea9d404cb974572c5e52554c09186993d4d56719b /src
parent615938651d3a4fd9253b08da00db22d451a8cef8 (diff)
Fix dropping of all capabilities
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.
Diffstat (limited to 'src')
-rw-r--r--src/shared/capability.c32
1 files changed, 16 insertions, 16 deletions
diff --git a/src/shared/capability.c b/src/shared/capability.c
index b39e8e2359..dcf7ce1a69 100644
--- a/src/shared/capability.c
+++ b/src/shared/capability.c
@@ -230,7 +230,6 @@ int capability_bounding_set_drop_usermode(uint64_t drop) {
}
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;
@@ -248,8 +247,8 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
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);
@@ -264,26 +263,27 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
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();
- 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");
+ }
return 0;
}