[PATCH] p9caps: add Plan9 capability devices

Enrico Weigelt, metux IT consult
2018-02-10T16:58:49Z

From: "Enrico Weigelt, metux IT consult" <info@metux.net>

This driver implements the Plan9 capability devices, used for
switching user id via capability tokens.

https://9p.io/sys/doc/auth.html
---
drivers/staging/Kconfig | 2 +
drivers/staging/Makefile | 1 +
drivers/staging/p9caps/Kconfig | 11 ++
drivers/staging/p9caps/Makefile | 1 +
drivers/staging/p9caps/p9caps.c | 371 ++++++++++++++++++++++++++++++++++++++++
5 files changed, 386 insertions(+)
create mode 100644 drivers/staging/p9caps/Kconfig
create mode 100644 drivers/staging/p9caps/Makefile
create mode 100644 drivers/staging/p9caps/p9caps.c

diff --git a/drivers/staging/Kconfig b/drivers/staging/Kconfig
index 554683912cff..23f325339fe8 100644
--- a/drivers/staging/Kconfig
+++ b/drivers/staging/Kconfig
@@ -118,4 +118,6 @@ source "drivers/staging/vboxvideo/Kconfig"

source "drivers/staging/pi433/Kconfig"

+source "drivers/staging/p9caps/Kconfig"
+
endif # STAGING
diff --git a/drivers/staging/Makefile b/drivers/staging/Makefile
index 6e536020029a..eccdf4643453 100644
--- a/drivers/staging/Makefile
+++ b/drivers/staging/Makefile
@@ -3,6 +3,7 @@

obj-y += media/
obj-y += typec/
+obj-$(CONFIG_PLAN9CAPS) += p9caps/
obj-$(CONFIG_IRDA) += irda/net/
obj-$(CONFIG_IRDA) += irda/drivers/
obj-$(CONFIG_PRISM2_USB) += wlan-ng/
diff --git a/drivers/staging/p9caps/Kconfig b/drivers/staging/p9caps/Kconfig
new file mode 100644
index 000000000000..455c3fa726ff
--- /dev/null
+++ b/drivers/staging/p9caps/Kconfig
@@ -0,0 +1,11 @@
+config PLAN9CAPS
+ tristate "Plan 9 capability device"
+ default n
+ select CRYPTO_HMAC
+ select CRYPTO_SHA1
+ help
+ This module implements the Plan 9 capability devices
+ /dev/caphash and /dev/capuse
+
+ To compile this driver as a module, choose
+ M here: the module will be called p9auth.
diff --git a/drivers/staging/p9caps/Makefile b/drivers/staging/p9caps/Makefile
new file mode 100644
index 000000000000..67d38099a249
--- /dev/null
+++ b/drivers/staging/p9caps/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_PLAN9CAPS) += p9caps.o
diff --git a/drivers/staging/p9caps/p9caps.c b/drivers/staging/p9caps/p9caps.c
new file mode 100644
index 000000000000..4c5c94dc1893
--- /dev/null
+++ b/drivers/staging/p9caps/p9caps.c
@@ -0,0 +1,371 @@
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/errno.h>
+#include <linux/fcntl.h>
+#include <linux/cdev.h>
+#include <linux/list.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/scatterlist.h>
+#include <linux/cred.h>
+#include <linux/err.h>
+#include <linux/user_namespace.h>
+#include <linux/mutex.h>
+#include <crypto/hash.h>
+#include <crypto/sha.h>
+
+/*
+ * Plan9 /dev/caphash and /dev/capuse device
+ *
+ * 2DO: - caphash should only allow one process (per userns)
+ * - support textual user names
+ * - invalidate old caps
+ */
+
+#define DEVICE_CAPUSE "/dev/capuse"
+#define DEVICE_CAPHASH "/dev/caphash"
+
+#define MODNAME "p9cap"
+
+struct caphash_entry {
+ struct list_head list;
+ struct user_namespace *user_ns;
+ char data[SHA1_DIGEST_SIZE];
+};
+
+struct caphash_writer {
+ struct list_head list;
+ struct user_namespace *user_ns;
+};
+
+static dev_t caphash_devid = 0;
+static dev_t capuse_devid = 0;
+
+static LIST_HEAD(caphash_entries);
+static LIST_HEAD(caphash_writers);
+
+static DEFINE_MUTEX(p9cap_lock);
+
+struct crypto_ahash *p9cap_tfm = NULL;
+
+static int caphash_open(struct inode *inode, struct file *filp)
+{
+ struct caphash_writer *tmp = NULL;
+ struct user_namespace *user_ns = current_user_ns();
+ int retval = 0;
+ struct list_head *pos, *q;
+
+ /* make sure only one instance per namespace can be opened */
+ mutex_lock(&p9cap_lock);
+
+ list_for_each_safe(pos, q, &(caphash_writers)) {
+ tmp = list_entry(pos, struct caphash_writer, list);
+ if (tmp->user_ns == user_ns) {
+ printk(KERN_ERR DEVICE_CAPHASH ": already locked in this namespace\n");
+ retval = -EBUSY;
+ goto out;
+ }
+ }
+
+ if (!(tmp = kzalloc(sizeof(struct caphash_writer), GFP_KERNEL))) {
+ retval = -ENOMEM;
+ goto out;
+ }
+
+ tmp->user_ns = get_user_ns(user_ns);
+ list_add(&(tmp->list), &caphash_writers);
+
+out:
+ mutex_unlock(&p9cap_lock);
+ return retval;
+}
+
+static int caphash_release(struct inode *inode, struct file *filp)
+{
+ int retval = 0;
+ struct user_namespace *user_ns = current_user_ns();
+ struct list_head *pos, *q;
+ struct caphash_entry *tmp;
+
+ mutex_lock(&p9cap_lock);
+
+ list_for_each_safe(pos, q, &(caphash_writers)) {
+ tmp = list_entry(pos, struct caphash_entry, list);
+ if (tmp->user_ns == user_ns) {
+ list_del(pos);
+ kfree(tmp);
+ goto out;
+ }
+ }
+
+out:
+ mutex_unlock(&p9cap_lock);
+ return retval;
+}
+
+static ssize_t caphash_write(struct file *filp, const char __user *buf,
+ size_t count, loff_t *f_pos)
+{
+ struct caphash_entry *ent;
+
+ if (count > SHA1_DIGEST_SIZE) {
+ printk(KERN_ERR DEVICE_CAPHASH ": too large: %d\n", count);
+ return -E2BIG;
+ }
+
+ if (!(ent = kzalloc(sizeof(struct caphash_entry), GFP_KERNEL)))
+ return -ENOMEM;
+
+ if (copy_from_user(&(ent->data), buf, count)) {
+ kfree(ent);
+ return -EFAULT;
+ }
+
+ ent->user_ns = get_user_ns(current_user_ns());
+
+ mutex_lock(&p9cap_lock);
+ list_add(&(ent->list), &caphash_entries);
+ mutex_unlock(&p9cap_lock);
+
+ return count;
+}
+
+/* called w/ lock held. we can releave this by allocating tfm locally */
+static ssize_t hash(const char *src, const char* dst, const char *key, u8 *result)
+{
+ struct scatterlist sg;
+ struct ahash_request *req;
+ int retval;
+ char *text = NULL;
+ size_t text_len;
+ int digest_len;
+ u8* digest = NULL;
+
+ text_len = strlen(src)+strlen(dst)+1; /* src@dst\0 */
+ digest_len = crypto_ahash_reqsize(p9cap_tfm);
+
+ digest = kzalloc(digest_len, GFP_KERNEL);
+ text = kzalloc(text_len+1, GFP_KERNEL);
+
+ if (!digest || !text) {
+ retval = -ENOMEM;
+ goto out;
+ }
+
+ if (!(req = ahash_request_alloc(p9cap_tfm, GFP_KERNEL))) {
+ printk(KERN_ERR MODNAME ": failed to alloc ahash_request\n");
+ retval = -ENOMEM;
+ goto out;
+ }
+
+ snprintf(text, text_len+1, "%s@%s", src, dst);
+ sg_set_buf(&sg, text, text_len);
+
+ ahash_request_set_callback(req, 0, NULL, NULL);
+ ahash_request_set_crypt(req, &sg, digest, text_len);
+
+ if ((retval = crypto_ahash_setkey(p9cap_tfm, key, strlen(key)))) {
+ printk(KERN_ERR MODNAME ": crypto_ahash_setkey() failed ret=%d\n", retval);
+ goto out;
+ }
+
+ if ((retval = crypto_ahash_digest(req))) {
+ printk(KERN_ERR MODNAME ": digest() failed ret=%d\n", retval);
+ goto out;
+ }
+
+ memcpy(result, digest, SHA1_DIGEST_SIZE);
+
+out:
+ kfree(text);
+ kfree(digest);
+
+ return 0;
+}
+
+static inline kuid_t convert_uid(const char* uname)
+{
+ return make_kuid(current_user_ns(), simple_strtol(uname, NULL, 0));
+}
+
+static ssize_t switch_uid(const char *src_uname, const char *dst_uname)
+{
+ struct cred *creds = prepare_creds();
+
+ kuid_t src_uid = convert_uid(src_uname);
+ kuid_t dst_uid = convert_uid(dst_uname);
+
+ if (!uid_eq(src_uid, current_uid())) {
+ printk(KERN_INFO DEVICE_CAPUSE ": src uid mismatch\n");
+ return -EPERM;
+ }
+
+ if (!(creds = prepare_creds()))
+ return -ENOMEM;
+
+ creds->uid = dst_uid;
+ creds->euid = dst_uid;
+
+ printk(KERN_INFO DEVICE_CAPUSE ": switching from kuid %d to %d\n", src_uid.val, dst_uid.val);
+ return commit_creds(creds);
+}
+
+static ssize_t try_switch(const char* src_uname, const char* dst_uname, const u8* hashval)
+{
+ struct list_head *pos;
+ list_for_each(pos, &(caphash_entries)) {
+ struct caphash_entry *tmp = list_entry(pos, struct caphash_entry, list);
+ if ((0 == memcmp(hashval, tmp->data, SHA1_DIGEST_SIZE)) &&
+ (tmp->user_ns == current_user_ns())) {
+
+ int retval;
+
+ if ((retval = switch_uid(src_uname, dst_uname))) {
+ printk(KERN_INFO DEVICE_CAPUSE ": uid switch failed\n");
+ return retval;
+ }
+
+ tmp = list_entry(pos, struct caphash_entry, list);
+ list_del(pos);
+ put_user_ns(tmp->user_ns);
+ kfree(tmp);
+
+ return 0;
+ }
+ }
+
+ printk(KERN_INFO DEVICE_CAPUSE ": cap not found\n");
+
+ return -ENOENT;
+}
+
+static ssize_t capuse_write(struct file *filp, const char __user *buf,
+ size_t count, loff_t *f_pos)
+{
+ ssize_t retval = count;
+ char *rand_str, *src_uname, *dst_uname;
+ u8 hashval[SHA1_DIGEST_SIZE] = { 0 };
+ char *cmdbuf;
+
+ if (!(cmdbuf = kzalloc(count, GFP_KERNEL)))
+ return -ENOMEM;
+
+ if (copy_from_user(cmdbuf, buf, count)) {
+ retval = -EFAULT;
+ goto out_free;
+ }
+
+ {
+ char *walk = cmdbuf;
+ src_uname = strsep(&walk, "@");
+ dst_uname = strsep(&walk, "@");
+ rand_str = walk;
+ if (!src_uname || !dst_uname || !rand_str) {
+ retval = -EINVAL;
+ goto out_free;
+ }
+ }
+
+ mutex_lock(&p9cap_lock);
+
+ if ((retval = hash(src_uname, dst_uname, rand_str, hashval)))
+ goto out_unlock;
+
+ if ((retval = try_switch(src_uname, dst_uname, hashval)))
+ goto out_unlock;
+
+ retval = count;
+
+out_unlock:
+ mutex_unlock(&p9cap_lock);
+
+out_free:
+ kfree(cmdbuf);
+ return retval;
+}
+
+static const struct file_operations p9cap_caphash_fops = {
+ .owner = THIS_MODULE,
+ .write = caphash_write,
+ .open = caphash_open,
+ .release = caphash_release,
+};
+
+static const struct file_operations p9cap_capuse_fops = {
+ .owner = THIS_MODULE,
+ .write = capuse_write,
+};
+
+static struct cdev p9cap_dev_caphash;
+static struct cdev p9cap_dev_capuse;
+
+static int p9cap_clear(void)
+{
+ struct caphash_entry *tmp;
+ struct list_head *pos, *q;
+
+ list_for_each_safe(pos, q, &(caphash_entries)) {
+ tmp = list_entry(pos, struct caphash_entry, list);
+ list_del(pos);
+ kfree(tmp);
+ }
+
+ return 0;
+}
+
+static void p9cap_cleanup_module(void)
+{
+ p9cap_clear();
+
+ cdev_del(&p9cap_dev_caphash);
+ cdev_del(&p9cap_dev_capuse);
+
+ unregister_chrdev_region(caphash_devid, 1);
+ unregister_chrdev_region(capuse_devid, 1);
+
+ if (p9cap_tfm)
+ crypto_free_ahash(p9cap_tfm);
+}
+
+static int p9cap_init_module(void)
+{
+ int retval;
+
+ p9cap_tfm = crypto_alloc_ahash("hmac(sha1)", 0, CRYPTO_ALG_ASYNC);
+ if (IS_ERR(p9cap_tfm)) {
+ retval = -PTR_ERR(p9cap_tfm);
+ printk(KERN_ERR MODNAME ": failed to load transform for hmac(sha1): %d\n", retval);
+ goto fail;
+ }
+
+ if ((retval = alloc_chrdev_region(&caphash_devid, 0, 1, DEVICE_CAPHASH)))
+ goto fail;
+
+ if ((retval = alloc_chrdev_region(&capuse_devid, 0, 1, DEVICE_CAPUSE)))
+ goto fail;
+
+ cdev_init(&p9cap_dev_caphash, &p9cap_caphash_fops);
+ p9cap_dev_caphash.owner = THIS_MODULE;
+ if ((retval = cdev_add(&p9cap_dev_caphash, caphash_devid, 1)))
+ printk(KERN_ERR MODNAME ": failed adding " DEVICE_CAPHASH ": %d\n", retval);
+
+ cdev_init(&p9cap_dev_capuse, &p9cap_capuse_fops);
+ p9cap_dev_capuse.owner = THIS_MODULE;
+ if ((retval = cdev_add(&p9cap_dev_capuse, capuse_devid, 1)))
+ printk(KERN_ERR MODNAME ": failed adding " DEVICE_CAPUSE ": %d\n", retval);
+
+ return 0;
+
+fail:
+ p9cap_cleanup_module();
+ return retval;
+}
+
+MODULE_AUTHOR("Enrico Weigelt, metux IT consult <info@metux.net>");
+MODULE_LICENSE("GPLv3");
+
+module_init(p9cap_init_module);
+module_exit(p9cap_cleanup_module);
--
2.11.0