From: Herbert Xu <herbert.xu@xxxxxxxxxx>
This patch introduces a hook mechanism to drivers/char/random
to allow the reads on /dev/*random as well as getrandom(2) to
be overridden by an external RNG.
This will be used to override drivers/char/random with a FIPS
RNG in a subsequent patch.
Signed-off-by: Herbert Xu <herbert.xu@xxxxxxxxxx>
Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
[6.1: Handle some context in getrandom() and random.h, and convert the
extrng_*_fops to use random_write_iter().]
Signed-off-by: Samuel Mendoza-Jonas <samjonas@xxxxxxxxxx>
[6.12: Further resolve surrounding conflicts in getrandom() and random.h.]
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Elena Avila <ellavila@xxxxxxxxxx>
---
drivers/char/random.c | 114 +++++++++++++++++++++++++++++++++++++++++
include/linux/random.h | 7 +++
2 files changed, 121 insertions(+)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 23ee76bbb4aa..032c5ffa814c 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -54,6 +54,7 @@
#include <linux/suspend.h>
#include <linux/siphash.h>
#include <linux/sched/isolation.h>
+#include <linux/rcupdate.h>
#include <crypto/chacha.h>
#include <crypto/blake2s.h>
#ifdef CONFIG_VDSO_GETRANDOM
@@ -330,6 +331,11 @@ static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],
memzero_explicit(first_block, sizeof(first_block));
}
+/*
+ * Hook for external RNG.
+ */
+static const struct random_extrng __rcu *extrng;
+
/*
* This function returns a ChaCha state that you may use for generating
* random data. It also returns up to 32 bytes on its own of random data
@@ -610,6 +616,9 @@ int __cold random_prepare_cpu(unsigned int cpu)
#endif
+static const struct file_operations extrng_random_fops;
+static const struct file_operations extrng_urandom_fops;
+
/**********************************************************************
*
* Entropy accumulation and extraction routines.
@@ -980,6 +989,19 @@ void __init add_bootloader_randomness(const void *buf, size_t len)
credit_init_bits(len * 8);
}
+void random_register_extrng(const struct random_extrng *rng)
+{
+ rcu_assign_pointer(extrng, rng);
+}
+EXPORT_SYMBOL_GPL(random_register_extrng);
+
+void random_unregister_extrng(void)
+{
+ RCU_INIT_POINTER(extrng, NULL);
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(random_unregister_extrng);
+
#if IS_ENABLED(CONFIG_VMGENID)
static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
@@ -1387,6 +1409,7 @@ static void __cold try_to_generate_entropy(void)
SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
{
+ const struct random_extrng *rng;
struct iov_iter iter;
int ret;
@@ -1400,6 +1423,18 @@ SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags
if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
return -EINVAL;
+ rcu_read_lock();
+ rng = rcu_dereference(extrng);
+ if (rng && !try_module_get(rng->owner))
+ rng = NULL;
+ rcu_read_unlock();
+
+ if (rng) {
+ ret = rng->extrng_read(ubuf, len);
+ module_put(rng->owner);
+ return ret;
+ }
+
if (!crng_ready() && !(flags & GRND_INSECURE)) {
if (flags & GRND_NONBLOCK)
return -EAGAIN;
@@ -1420,6 +1455,13 @@ static __poll_t random_poll(struct file *file, poll_table *wait)
return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
}
+static __poll_t
+extrng_poll(struct file *file, poll_table * wait)
+{
+ /* extrng pool is always full, always read, no writes */
+ return EPOLLIN | EPOLLRDNORM;
+}
+
static ssize_t write_pool_user(struct iov_iter *iter)
{
u8 block[BLAKE2S_BLOCK_SIZE];
@@ -1560,9 +1602,60 @@ static int random_fasync(int fd, struct file *filp, int on)
return fasync_helper(fd, filp, on, &fasync);
}
+static int random_open(struct inode *inode, struct file *filp)
+{
+ const struct random_extrng *rng;
+
+ rcu_read_lock();
+ rng = rcu_dereference(extrng);
+ if (rng && !try_module_get(rng->owner))
+ rng = NULL;
+ rcu_read_unlock();
+
+ if (!rng)
+ return 0;
+
+ filp->f_op = &extrng_random_fops;
+ filp->private_data = rng->owner;
+
+ return 0;
+}
+
+static int urandom_open(struct inode *inode, struct file *filp)
+{
+ const struct random_extrng *rng;
+
+ rcu_read_lock();
+ rng = rcu_dereference(extrng);
+ if (rng && !try_module_get(rng->owner))
+ rng = NULL;
+ rcu_read_unlock();
+
+ if (!rng)
+ return 0;
+
+ filp->f_op = &extrng_urandom_fops;
+ filp->private_data = rng->owner;
+
+ return 0;
+}
+
+static int extrng_release(struct inode *inode, struct file *filp)
+{
+ module_put(filp->private_data);
+ return 0;
+}
+
+static ssize_t
+extrng_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
+{
+ return rcu_dereference_raw(extrng)->extrng_read(buf, nbytes);
+}
+
const struct file_operations random_fops = {
.read_iter = random_read_iter,
.write_iter = random_write_iter,
+ .open = random_open,
.poll = random_poll,
.unlocked_ioctl = random_ioctl,
.compat_ioctl = compat_ptr_ioctl,
@@ -1575,6 +1668,7 @@ const struct file_operations random_fops = {
const struct file_operations urandom_fops = {
.read_iter = urandom_read_iter,
.write_iter = random_write_iter,
+ .open = urandom_open,
.unlocked_ioctl = random_ioctl,
.compat_ioctl = compat_ptr_ioctl,
.fasync = random_fasync,
@@ -1583,6 +1677,26 @@ const struct file_operations urandom_fops = {
.splice_write = iter_file_splice_write,
};
+static const struct file_operations extrng_random_fops = {
+ .open = random_open,
+ .read = extrng_read,
+ .write_iter = random_write_iter,
+ .poll = extrng_poll,
+ .unlocked_ioctl = random_ioctl,
+ .fasync = random_fasync,
+ .llseek = noop_llseek,
+ .release = extrng_release,
+};
+
+static const struct file_operations extrng_urandom_fops = {
+ .open = urandom_open,
+ .read = extrng_read,
+ .write_iter = random_write_iter,
+ .unlocked_ioctl = random_ioctl,
+ .fasync = random_fasync,
+ .llseek = noop_llseek,
+ .release = extrng_release,
+};
/********************************************************************
*
diff --git a/include/linux/random.h b/include/linux/random.h
index b0a940af4fff..6cfb75741ade 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -9,6 +9,11 @@
#include <uapi/linux/random.h>
+struct random_extrng {
+ ssize_t (*extrng_read)(void __user *buf, size_t buflen);
+ struct module *owner;
+};
+
struct notifier_block;
void add_device_randomness(const void *buf, size_t len);
@@ -120,6 +125,8 @@ void __init random_init(void);
bool rng_is_initialized(void);
int wait_for_random_bytes(void);
int execute_with_initialized_rng(struct notifier_block *nb);
+void random_register_extrng(const struct random_extrng *rng);
+void random_unregister_extrng(void);
/* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes).
* Returns the result of the call to wait_for_random_bytes. */
--
2.47.1
