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authorLaurent Vivier <lvivier@redhat.com>2019-09-12 15:30:22 +0200
committerHerbert Xu <herbert@gondor.apana.org.au>2019-10-10 23:36:31 +1100
commitdaae28debcb03eee837fadfd20788107b325c5a2 (patch)
tree75eb8010d01d55bfe0b67aa4688cbcba7e613f39
parenteff9771d51529acf7f6f58a60b2923b98da28f0e (diff)
downloadlinux-daae28debcb03eee837fadfd20788107b325c5a2.tar.bz2
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>
-rw-r--r--drivers/char/hw_random/core.c60
1 files changed, 44 insertions, 16 deletions
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 80b850ef1bf6..29f50c045c92 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -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);