From daae28debcb03eee837fadfd20788107b325c5a2 Mon Sep 17 00:00:00 2001 From: Laurent Vivier Date: Thu, 12 Sep 2019 15:30:22 +0200 Subject: [PATCH] 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 Signed-off-by: Herbert Xu --- drivers/char/hw_random/core.c | 60 +++++++++++++++++++++++++++++++------------ 1 file changed, 44 insertions(+), 16 deletions(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 80b850e..29f50c0 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(¤t_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); -- 2.7.4