cifs: Add idmap key and related data structures and functions (try #17 repost)

Define (global) data structures to store ids, uids and gids, to which a
SID maps.  There are two separate trees, one for SID/uid and another one
for SID/gid.

A new type of key, cifs_idmap_key_type, is used.

Keys are instantiated and searched using credential of the root by
overriding and restoring the credentials of the caller requesting the key.

Id mapping functions are invoked under config option of cifs acl.

Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 138 insertions, 0 deletions

diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
index a0d11eab14e5..061fc3afd841 100644
--- a/fs/cifs/cifsacl.c
+++ b/fs/cifs/cifsacl.c
@@ -23,6 +23,10 @@
 
 #include <linux/fs.h>
 #include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/keyctl.h>
+#include <linux/key-type.h>
+#include <keys/user-type.h>
 #include "cifspdu.h"
 #include "cifsglob.h"
 #include "cifsacl.h"
@@ -50,6 +54,140 @@ static const struct cifs_sid sid_authusers = {
 /* group users */
 static const struct cifs_sid sid_user = {1, 2 , {0, 0, 0, 0, 0, 5}, {} };
 
+static const struct cred *root_cred;
+
+/*
+ * Run idmap cache shrinker.
+ */
+static int
+cifs_idmap_shrinker(struct shrinker *shrink, int nr_to_scan, gfp_t gfp_mask)
+{
+        /* Use a pruning scheme in a subsequent patch instead */
+        cifs_destroy_idmaptrees();
+        return 0;
+}
+
+static struct shrinker cifs_shrinker = {
+        .shrink = cifs_idmap_shrinker,
+        .seeks = DEFAULT_SEEKS,
+};
+
+static int
+cifs_idmap_key_instantiate(struct key *key, const void *data, size_t datalen)
+{
+        char *payload;
+
+        payload = kmalloc(datalen, GFP_KERNEL);
+        if (!payload)
+                return -ENOMEM;
+
+        memcpy(payload, data, datalen);
+        key->payload.data = payload;
+        return 0;
+}
+
+static inline void
+cifs_idmap_key_destroy(struct key *key)
+{
+        kfree(key->payload.data);
+}
+
+static
+struct key_type cifs_idmap_key_type = {
+        .name        = "cifs.cifs_idmap",
+        .instantiate = cifs_idmap_key_instantiate,
+        .destroy     = cifs_idmap_key_destroy,
+        .describe    = user_describe,
+        .match       = user_match,
+};
+
+int
+init_cifs_idmap(void)
+{
+        struct cred *cred;
+        struct key *keyring;
+        int ret;
+
+        cFYI(1, "Registering the %s key type\n", cifs_idmap_key_type.name);
+
+        /* create an override credential set with a special thread keyring in
+         * which requests are cached
+         *
+         * this is used to prevent malicious redirections from being installed
+         * with add_key().
+         */
+        cred = prepare_kernel_cred(NULL);
+        if (!cred)
+                return -ENOMEM;
+
+        keyring = key_alloc(&key_type_keyring, ".cifs_idmap", 0, 0, cred,
+                            (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+                            KEY_USR_VIEW | KEY_USR_READ,
+                            KEY_ALLOC_NOT_IN_QUOTA);
+        if (IS_ERR(keyring)) {
+                ret = PTR_ERR(keyring);
+                goto failed_put_cred;
+        }
+
+        ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
+        if (ret < 0)
+                goto failed_put_key;
+
+        ret = register_key_type(&cifs_idmap_key_type);
+        if (ret < 0)
+                goto failed_put_key;
+
+        /* instruct request_key() to use this special keyring as a cache for
+         * the results it looks up */
+        cred->thread_keyring = keyring;
+        cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
+        root_cred = cred;
+
+        spin_lock_init(&siduidlock);
+        uidtree = RB_ROOT;
+        spin_lock_init(&sidgidlock);
+        gidtree = RB_ROOT;
+
+        register_shrinker(&cifs_shrinker);
+
+        cFYI(1, "cifs idmap keyring: %d\n", key_serial(keyring));
+        return 0;
+
+failed_put_key:
+        key_put(keyring);
+failed_put_cred:
+        put_cred(cred);
+        return ret;
+}
+
+void
+exit_cifs_idmap(void)
+{
+        key_revoke(root_cred->thread_keyring);
+        unregister_key_type(&cifs_idmap_key_type);
+        put_cred(root_cred);
+        unregister_shrinker(&cifs_shrinker);
+        cFYI(1, "Unregistered %s key type\n", cifs_idmap_key_type.name);
+}
+
+void
+cifs_destroy_idmaptrees(void)
+{
+        struct rb_root *root;
+        struct rb_node *node;
+
+        root = &uidtree;
+        spin_lock(&siduidlock);
+        while ((node = rb_first(root)))
+                rb_erase(node, root);
+        spin_unlock(&siduidlock);
+
+        root = &gidtree;
+        spin_lock(&sidgidlock);
+        while ((node = rb_first(root)))
+                rb_erase(node, root);
+        spin_unlock(&sidgidlock);
+}
 
 int match_sid(struct cifs_sid *ctsid)
 {