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>

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)
 {

fs/cifs/cifsfs.c

@@ -1033,22 +1033,31 @@ init_cifs(void)
 	if (rc)
 		goto out_destroy_mids;
 
-	rc = register_filesystem(&cifs_fs_type);
-	if (rc)
-		goto out_destroy_request_bufs;
 #ifdef CONFIG_CIFS_UPCALL
 	rc = register_key_type(&cifs_spnego_key_type);
 	if (rc)
-		goto out_unregister_filesystem;
-#endif
+		goto out_destroy_request_bufs;
+#endif /* CONFIG_CIFS_UPCALL */
+
+#ifdef CONFIG_CIFS_ACL
+	rc = init_cifs_idmap();
+	if (rc)
+		goto out_destroy_request_bufs;
+#endif /* CONFIG_CIFS_ACL */
+
+	rc = register_filesystem(&cifs_fs_type);
+	if (rc)
+		goto out_destroy_request_bufs;
 
 	return 0;
 
+out_destroy_request_bufs:
+#ifdef CONFIG_CIFS_ACL
+	exit_cifs_idmap();
+#endif
 #ifdef CONFIG_CIFS_UPCALL
-out_unregister_filesystem:
-	unregister_filesystem(&cifs_fs_type);
+	unregister_key_type(&cifs_spnego_key_type);
 #endif
-out_destroy_request_bufs:
 	cifs_destroy_request_bufs();
 out_destroy_mids:
 	cifs_destroy_mids();
@@ -1070,6 +1079,10 @@ exit_cifs(void)
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	cifs_dfs_release_automount_timer();
 #endif
+#ifdef CONFIG_CIFS_ACL
+	cifs_destroy_idmaptrees();
+	exit_cifs_idmap();
+#endif
 #ifdef CONFIG_CIFS_UPCALL
 	unregister_key_type(&cifs_spnego_key_type);
 #endif

fs/cifs/cifsglob.h

@@ -833,6 +833,11 @@ GLOBAL_EXTERN unsigned int cifs_max_pending; /* MAX requests at once to server*/
 /* reconnect after this many failed echo attempts */
 GLOBAL_EXTERN unsigned short echo_retries;
 
+GLOBAL_EXTERN struct rb_root uidtree;
+GLOBAL_EXTERN struct rb_root gidtree;
+GLOBAL_EXTERN spinlock_t siduidlock;
+GLOBAL_EXTERN spinlock_t sidgidlock;
+
 void cifs_oplock_break(struct work_struct *work);
 void cifs_oplock_break_get(struct cifsFileInfo *cfile);
 void cifs_oplock_break_put(struct cifsFileInfo *cfile);

fs/cifs/cifsproto.h

@@ -53,6 +53,9 @@ do {								\
 	cFYI(1, "CIFS VFS: leaving %s (xid = %d) rc = %d",	\
 	     __func__, curr_xid, (int)rc);			\
 } while (0)
+extern int init_cifs_idmap(void);
+extern void exit_cifs_idmap(void);
+extern void cifs_destroy_idmaptrees(void);
 extern char *build_path_from_dentry(struct dentry *);
 extern char *cifs_build_path_to_root(struct cifs_sb_info *cifs_sb,
 					struct cifsTconInfo *tcon);