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From: David Herrmann <dh.herrmann@gmail.com>
Date: Wed, 22 Apr 2015 13:14:24 +0200
Subject: [PATCH] kdbus: translate capabilities between namespaces
Right now, we always drop capability-items if we cross user-namespaces.
However, the kernel _does_ support capability translation, as defined in
./security/commoncap.c cap_capable().
This patch adds capability translation support just like cap_capable()
does. This way, a message sent from a task into a child user-namespace of
its own, will retain the capability-item and thus keep the parent
privileged inside of the user-namespace of its children.
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
---
ipc/kdbus/metadata.c | 126 ++++++++++++++++++++++++++++++++++-----------------
1 file changed, 84 insertions(+), 42 deletions(-)
diff --git a/ipc/kdbus/metadata.c b/ipc/kdbus/metadata.c
index b908b6314a00..7949c8d3ed64 100644
--- a/ipc/kdbus/metadata.c
+++ b/ipc/kdbus/metadata.c
@@ -63,8 +63,7 @@
* @root_path: Root-FS path
* @cmdline: Command-line
* @cgroup: Full cgroup path
- * @caps: Capabilities
- * @caps_namespace: User-namespace of @caps
+ * @cred: Credentials
* @seclabel: Seclabel
* @audit_loginuid: Audit login-UID
* @audit_sessionid: Audit session-ID
@@ -104,14 +103,7 @@ struct kdbus_meta_proc {
char *cgroup;
/* KDBUS_ITEM_CAPS */
- struct caps {
- /* binary compatible to kdbus_caps */
- u32 last_cap;
- struct {
- u32 caps[_KERNEL_CAPABILITY_U32S];
- } set[4];
- } caps;
- struct user_namespace *caps_namespace;
+ const struct cred *cred;
/* KDBUS_ITEM_SECLABEL */
char *seclabel;
@@ -149,6 +141,14 @@ struct kdbus_meta_conn {
char *conn_description;
};
+/* fixed size equivalent of "kdbus_caps" */
+struct kdbus_meta_caps {
+ u32 last_cap;
+ struct {
+ u32 caps[_KERNEL_CAPABILITY_U32S];
+ } set[4];
+};
+
/**
* kdbus_meta_proc_new() - Create process metadata object
*
@@ -175,7 +175,8 @@ static void kdbus_meta_proc_free(struct kref *kref)
path_put(&mp->exe_path);
path_put(&mp->root_path);
- put_user_ns(mp->caps_namespace);
+ if (mp->cred)
+ put_cred(mp->cred);
put_pid(mp->ppid);
put_pid(mp->tgid);
put_pid(mp->pid);
@@ -354,25 +355,7 @@ static int kdbus_meta_proc_collect_cgroup(struct kdbus_meta_proc *mp)
static void kdbus_meta_proc_collect_caps(struct kdbus_meta_proc *mp)
{
- const struct cred *c = current_cred();
- int i;
-
- /* ABI: "last_cap" equals /proc/sys/kernel/cap_last_cap */
- mp->caps.last_cap = CAP_LAST_CAP;
- mp->caps_namespace = get_user_ns(current_user_ns());
-
- CAP_FOR_EACH_U32(i) {
- mp->caps.set[0].caps[i] = c->cap_inheritable.cap[i];
- mp->caps.set[1].caps[i] = c->cap_permitted.cap[i];
- mp->caps.set[2].caps[i] = c->cap_effective.cap[i];
- mp->caps.set[3].caps[i] = c->cap_bset.cap[i];
- }
-
- /* clear unused bits */
- for (i = 0; i < 4; i++)
- mp->caps.set[i].caps[CAP_TO_INDEX(CAP_LAST_CAP)] &=
- CAP_LAST_U32_VALID_MASK;
-
+ mp->cred = get_current_cred();
mp->valid |= KDBUS_ATTACH_CAPS;
}
@@ -880,7 +863,7 @@ int kdbus_meta_export_prepare(struct kdbus_meta_proc *mp,
size += KDBUS_ITEM_SIZE(strlen(mp->cgroup) + 1);
if (mp && (*mask & KDBUS_ATTACH_CAPS))
- size += KDBUS_ITEM_SIZE(sizeof(mp->caps));
+ size += KDBUS_ITEM_SIZE(sizeof(struct kdbus_meta_caps));
if (mp && (*mask & KDBUS_ATTACH_SECLABEL))
size += KDBUS_ITEM_SIZE(strlen(mp->seclabel) + 1);
@@ -917,6 +900,69 @@ static int kdbus_meta_push_kvec(struct kvec *kvec,
return 2 + !!kdbus_kvec_pad(kvec++, size);
}
+static void kdbus_meta_export_caps(struct kdbus_meta_caps *out,
+ struct kdbus_meta_proc *mp)
+{
+ struct user_namespace *iter;
+ const struct cred *cred = mp->cred;
+ bool parent = false, owner = false;
+ int i;
+
+ /*
+ * This translates the effective capabilities of 'cred' into the current
+ * user-namespace. If the current user-namespace is a child-namespace of
+ * the user-namespace of 'cred', the mask can be copied verbatim. If
+ * not, the mask is cleared.
+ * There's one exception: If 'cred' is the owner of any user-namespace
+ * in the path between the current user-namespace and the user-namespace
+ * of 'cred', then it has all effective capabilities set. This means,
+ * the user who created a user-namespace always has all effective
+ * capabilities in any child namespaces. Note that this is based on the
+ * uid of the namespace creator, not the task hierarchy.
+ */
+ for (iter = current_user_ns(); iter; iter = iter->parent) {
+ if (iter == cred->user_ns) {
+ parent = true;
+ break;
+ }
+
+ if (iter == &init_user_ns)
+ break;
+
+ if ((iter->parent == cred->user_ns) &&
+ uid_eq(iter->owner, cred->euid)) {
+ owner = true;
+ break;
+ }
+ }
+
+ out->last_cap = CAP_LAST_CAP;
+
+ CAP_FOR_EACH_U32(i) {
+ if (parent) {
+ out->set[0].caps[i] = cred->cap_inheritable.cap[i];
+ out->set[1].caps[i] = cred->cap_permitted.cap[i];
+ out->set[2].caps[i] = cred->cap_effective.cap[i];
+ out->set[3].caps[i] = cred->cap_bset.cap[i];
+ } else if (owner) {
+ out->set[0].caps[i] = 0U;
+ out->set[1].caps[i] = ~0U;
+ out->set[2].caps[i] = ~0U;
+ out->set[3].caps[i] = ~0U;
+ } else {
+ out->set[0].caps[i] = 0U;
+ out->set[1].caps[i] = 0U;
+ out->set[2].caps[i] = 0U;
+ out->set[3].caps[i] = 0U;
+ }
+ }
+
+ /* clear unused bits */
+ for (i = 0; i < 4; i++)
+ out->set[i].caps[CAP_TO_INDEX(CAP_LAST_CAP)] &=
+ CAP_LAST_U32_VALID_MASK;
+}
+
/* This is equivalent to from_kuid_munged(), but maps INVALID_UID to itself */
static uid_t kdbus_from_kuid_keep(kuid_t uid)
{
@@ -975,14 +1021,6 @@ int kdbus_meta_export(struct kdbus_meta_proc *mp,
hdr = &item_hdr[0];
- /*
- * TODO: We currently have no sane way of translating a set of caps
- * between different user namespaces. Until that changes, we have
- * to drop such items.
- */
- if (mp && mp->caps_namespace != user_ns)
- mask &= ~KDBUS_ATTACH_CAPS;
-
if (mask == 0) {
*real_size = 0;
return 0;
@@ -1088,10 +1126,14 @@ int kdbus_meta_export(struct kdbus_meta_proc *mp,
KDBUS_ITEM_CGROUP, mp->cgroup,
strlen(mp->cgroup) + 1, &size);
- if (mp && (mask & KDBUS_ATTACH_CAPS))
+ if (mp && (mask & KDBUS_ATTACH_CAPS)) {
+ struct kdbus_meta_caps caps = {};
+
+ kdbus_meta_export_caps(&caps, mp);
cnt += kdbus_meta_push_kvec(kvec + cnt, hdr++,
- KDBUS_ITEM_CAPS, &mp->caps,
- sizeof(mp->caps), &size);
+ KDBUS_ITEM_CAPS, &caps,
+ sizeof(caps), &size);
+ }
if (mp && (mask & KDBUS_ATTACH_SECLABEL))
cnt += kdbus_meta_push_kvec(kvec + cnt, hdr++,
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