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hwrng: core - move add_early_randomness() out of rng_mutex 

add_early_randomness() is called every time a new rng backend is added
and every time it is set as the current rng provider.

add_early_randomness() is called from functions locking rng_mutex,
and if it hangs all the hw_random framework hangs: we can't read sysfs,
add or remove a backend.

This patch move add_early_randomness() out of the rng_mutex zone.
It only needs the reading_mutex.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Laurent Vivier 2019-09-12 15:30:22 +02:00 committed by Herbert Xu
parent eff9771d51
commit daae28debc
1 changed files with 44 additions and 16 deletions
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60
drivers/char/hw_random/core.c
View File

@ -112,6 +112,14 @@ static void drop_current_rng(void)
}
/* Returns ERR_PTR(), NULL or refcounted hwrng */
static struct hwrng *get_current_rng_nolock(void)
{
if (current_rng)
kref_get(&current_rng->ref);
return current_rng;
}
static struct hwrng *get_current_rng(void)
{
struct hwrng *rng;
@ -119,9 +127,7 @@ static struct hwrng *get_current_rng(void)
if (mutex_lock_interruptible(&rng_mutex))
return ERR_PTR(-ERESTARTSYS);
rng = current_rng;
if (rng)
kref_get(&rng->ref);
rng = get_current_rng_nolock();
mutex_unlock(&rng_mutex);
return rng;
@ -156,8 +162,6 @@ static int hwrng_init(struct hwrng *rng)
reinit_completion(&rng->cleanup_done);
skip_init:
add_early_randomness(rng);
current_quality = rng->quality ? : default_quality;
if (current_quality > 1024)
current_quality = 1024;
@ -321,12 +325,13 @@ static ssize_t hwrng_attr_current_store(struct device *dev,
const char *buf, size_t len)
{
int err = -ENODEV;
struct hwrng *rng;
struct hwrng *rng, *old_rng, *new_rng;
err = mutex_lock_interruptible(&rng_mutex);
if (err)
return -ERESTARTSYS;
old_rng = current_rng;
if (sysfs_streq(buf, "")) {
err = enable_best_rng();
} else {
@ -338,9 +343,15 @@ static ssize_t hwrng_attr_current_store(struct device *dev,
}
}
}
new_rng = get_current_rng_nolock();
mutex_unlock(&rng_mutex);
if (new_rng) {
if (new_rng != old_rng)
add_early_randomness(new_rng);
put_rng(new_rng);
}
return err ? : len;
}
@ -460,13 +471,17 @@ static void start_khwrngd(void)
int hwrng_register(struct hwrng *rng)
{
int err = -EINVAL;
struct hwrng *old_rng, *tmp;
struct hwrng *old_rng, *new_rng, *tmp;
struct list_head *rng_list_ptr;
if (!rng->name || (!rng->data_read && !rng->read))
goto out;
mutex_lock(&rng_mutex);
old_rng = current_rng;
new_rng = NULL;
/* Must not register two RNGs with the same name. */
err = -EEXIST;
list_for_each_entry(tmp, &rng_list, list) {
@ -485,7 +500,6 @@ int hwrng_register(struct hwrng *rng)
}
list_add_tail(&rng->list, rng_list_ptr);
old_rng = current_rng;
err = 0;
if (!old_rng ||
(!cur_rng_set_by_user && rng->quality > old_rng->quality)) {
@ -499,19 +513,24 @@ int hwrng_register(struct hwrng *rng)
goto out_unlock;
}
if (old_rng && !rng->init) {
new_rng = rng;
kref_get(&new_rng->ref);
out_unlock:
mutex_unlock(&rng_mutex);
if (new_rng) {
if (new_rng != old_rng || !rng->init) {
/*
* Use a new device's input to add some randomness to
* the system. If this rng device isn't going to be
* used right away, its init function hasn't been
* called yet; so only use the randomness from devices
* that don't need an init callback.
* called yet by set_current_rng(); so only use the
* randomness from devices that don't need an init callback
*/
add_early_randomness(rng);
add_early_randomness(new_rng);
}
put_rng(new_rng);
}
out_unlock:
mutex_unlock(&rng_mutex);
out:
return err;
}
@ -519,10 +538,12 @@ EXPORT_SYMBOL_GPL(hwrng_register);
void hwrng_unregister(struct hwrng *rng)
{
struct hwrng *old_rng, *new_rng;
int err;
mutex_lock(&rng_mutex);
old_rng = current_rng;
list_del(&rng->list);
if (current_rng == rng) {
err = enable_best_rng();
@ -532,6 +553,7 @@ void hwrng_unregister(struct hwrng *rng)
}
}
new_rng = get_current_rng_nolock();
if (list_empty(&rng_list)) {
mutex_unlock(&rng_mutex);
if (hwrng_fill)
@ -539,6 +561,12 @@ void hwrng_unregister(struct hwrng *rng)
} else
mutex_unlock(&rng_mutex);
if (new_rng) {
if (old_rng != new_rng)
add_early_randomness(new_rng);
put_rng(new_rng);
}
wait_for_completion(&rng->cleanup_done);
}
EXPORT_SYMBOL_GPL(hwrng_unregister);