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authorDavid Howells <dhowells@redhat.com>2013-09-24 10:35:18 +0100
committerDavid Howells <dhowells@redhat.com>2013-09-24 10:35:18 +0100
commitab3c3587f8cda9083209a61dbe3a4407d3cada10 (patch)
treec479efb4b7a834ee5d3b74d81560a2214c463431
parentb2a4df200d570b2c33a57e1ebfa5896e4bc81b69 (diff)
KEYS: Implement a big key type that can save to tmpfs
Implement a big key type that can save its contents to tmpfs and thus swapspace when memory is tight. This is useful for Kerberos ticket caches. Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: Simo Sorce <simo@redhat.com>
-rw-r--r--include/keys/big_key-type.h25
-rw-r--r--include/linux/key.h1
-rw-r--r--security/keys/Kconfig11
-rw-r--r--security/keys/Makefile1
-rw-r--r--security/keys/big_key.c204
5 files changed, 242 insertions, 0 deletions
diff --git a/include/keys/big_key-type.h b/include/keys/big_key-type.h
new file mode 100644
index 000000000000..d69bc8af3292
--- /dev/null
+++ b/include/keys/big_key-type.h
@@ -0,0 +1,25 @@
+/* Big capacity key type.
+ *
+ * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#ifndef _KEYS_BIG_KEY_TYPE_H
+#define _KEYS_BIG_KEY_TYPE_H
+
+#include <linux/key-type.h>
+
+extern struct key_type key_type_big_key;
+
+extern int big_key_instantiate(struct key *key, struct key_preparsed_payload *prep);
+extern void big_key_revoke(struct key *key);
+extern void big_key_destroy(struct key *key);
+extern void big_key_describe(const struct key *big_key, struct seq_file *m);
+extern long big_key_read(const struct key *key, char __user *buffer, size_t buflen);
+
+#endif /* _KEYS_BIG_KEY_TYPE_H */
diff --git a/include/linux/key.h b/include/linux/key.h
index 2417f789d29b..010dbb618aca 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -201,6 +201,7 @@ struct key {
unsigned long value;
void __rcu *rcudata;
void *data;
+ void *data2[2];
} payload;
struct assoc_array keys;
};
diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index 15e0dfe8c80f..b56362275ec8 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -20,6 +20,17 @@ config KEYS
If you are unsure as to whether this is required, answer N.
+config BIG_KEYS
+ tristate "Large payload keys"
+ depends on KEYS
+ depends on TMPFS
+ help
+ This option provides support for holding large keys within the kernel
+ (for example Kerberos ticket caches). The data may be stored out to
+ swapspace by tmpfs.
+
+ If you are unsure as to whether this is required, answer N.
+
config TRUSTED_KEYS
tristate "TRUSTED KEYS"
depends on KEYS && TCG_TPM
diff --git a/security/keys/Makefile b/security/keys/Makefile
index 504aaa008388..c487c77a00be 100644
--- a/security/keys/Makefile
+++ b/security/keys/Makefile
@@ -22,5 +22,6 @@ obj-$(CONFIG_SYSCTL) += sysctl.o
#
# Key types
#
+obj-$(CONFIG_BIG_KEYS) += big_key.o
obj-$(CONFIG_TRUSTED_KEYS) += trusted.o
obj-$(CONFIG_ENCRYPTED_KEYS) += encrypted-keys/
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
new file mode 100644
index 000000000000..5f9defc4a807
--- /dev/null
+++ b/security/keys/big_key.c
@@ -0,0 +1,204 @@
+/* Large capacity key type
+ *
+ * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/seq_file.h>
+#include <linux/file.h>
+#include <linux/shmem_fs.h>
+#include <linux/err.h>
+#include <keys/user-type.h>
+#include <keys/big_key-type.h>
+
+MODULE_LICENSE("GPL");
+
+/*
+ * If the data is under this limit, there's no point creating a shm file to
+ * hold it as the permanently resident metadata for the shmem fs will be at
+ * least as large as the data.
+ */
+#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
+
+/*
+ * big_key defined keys take an arbitrary string as the description and an
+ * arbitrary blob of data as the payload
+ */
+struct key_type key_type_big_key = {
+ .name = "big_key",
+ .def_lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
+ .instantiate = big_key_instantiate,
+ .match = user_match,
+ .revoke = big_key_revoke,
+ .destroy = big_key_destroy,
+ .describe = big_key_describe,
+ .read = big_key_read,
+};
+
+/*
+ * Instantiate a big key
+ */
+int big_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
+{
+ struct path *path = (struct path *)&key->payload.data2;
+ struct file *file;
+ ssize_t written;
+ size_t datalen = prep->datalen;
+ int ret;
+
+ ret = -EINVAL;
+ if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
+ goto error;
+
+ /* Set an arbitrary quota */
+ ret = key_payload_reserve(key, 16);
+ if (ret < 0)
+ goto error;
+
+ key->type_data.x[1] = datalen;
+
+ if (datalen > BIG_KEY_FILE_THRESHOLD) {
+ /* Create a shmem file to store the data in. This will permit the data
+ * to be swapped out if needed.
+ *
+ * TODO: Encrypt the stored data with a temporary key.
+ */
+ file = shmem_file_setup("", datalen, 0);
+ if (IS_ERR(file))
+ goto err_quota;
+
+ written = kernel_write(file, prep->data, prep->datalen, 0);
+ if (written != datalen) {
+ if (written >= 0)
+ ret = -ENOMEM;
+ goto err_fput;
+ }
+
+ /* Pin the mount and dentry to the key so that we can open it again
+ * later
+ */
+ *path = file->f_path;
+ path_get(path);
+ fput(file);
+ } else {
+ /* Just store the data in a buffer */
+ void *data = kmalloc(datalen, GFP_KERNEL);
+ if (!data) {
+ ret = -ENOMEM;
+ goto err_quota;
+ }
+
+ key->payload.data = memcpy(data, prep->data, prep->datalen);
+ }
+ return 0;
+
+err_fput:
+ fput(file);
+err_quota:
+ key_payload_reserve(key, 0);
+error:
+ return ret;
+}
+
+/*
+ * dispose of the links from a revoked keyring
+ * - called with the key sem write-locked
+ */
+void big_key_revoke(struct key *key)
+{
+ struct path *path = (struct path *)&key->payload.data2;
+
+ /* clear the quota */
+ key_payload_reserve(key, 0);
+ if (key_is_instantiated(key) && key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD)
+ vfs_truncate(path, 0);
+}
+
+/*
+ * dispose of the data dangling from the corpse of a big_key key
+ */
+void big_key_destroy(struct key *key)
+{
+ if (key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD) {
+ struct path *path = (struct path *)&key->payload.data2;
+ path_put(path);
+ path->mnt = NULL;
+ path->dentry = NULL;
+ } else {
+ kfree(key->payload.data);
+ key->payload.data = NULL;
+ }
+}
+
+/*
+ * describe the big_key key
+ */
+void big_key_describe(const struct key *key, struct seq_file *m)
+{
+ unsigned long datalen = key->type_data.x[1];
+
+ seq_puts(m, key->description);
+
+ if (key_is_instantiated(key))
+ seq_printf(m, ": %lu [%s]",
+ datalen,
+ datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
+}
+
+/*
+ * read the key data
+ * - the key's semaphore is read-locked
+ */
+long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
+{
+ unsigned long datalen = key->type_data.x[1];
+ long ret;
+
+ if (!buffer || buflen < datalen)
+ return datalen;
+
+ if (datalen > BIG_KEY_FILE_THRESHOLD) {
+ struct path *path = (struct path *)&key->payload.data2;
+ struct file *file;
+ loff_t pos;
+
+ file = dentry_open(path, O_RDONLY, current_cred());
+ if (IS_ERR(file))
+ return PTR_ERR(file);
+
+ pos = 0;
+ ret = vfs_read(file, buffer, datalen, &pos);
+ fput(file);
+ if (ret >= 0 && ret != datalen)
+ ret = -EIO;
+ } else {
+ ret = datalen;
+ if (copy_to_user(buffer, key->payload.data, datalen) != 0)
+ ret = -EFAULT;
+ }
+
+ return ret;
+}
+
+/*
+ * Module stuff
+ */
+static int __init big_key_init(void)
+{
+ return register_key_type(&key_type_big_key);
+}
+
+static void __exit big_key_cleanup(void)
+{
+ unregister_key_type(&key_type_big_key);
+}
+
+module_init(big_key_init);
+module_exit(big_key_cleanup);

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