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hwrng: core - Fix current_rng init/cleanup race yet again 

The kref solution is still buggy because we were only focusing
on the register/unregister race.  The same race affects the
setting of current_rng through sysfs.

This patch fixes it by using kref_get_unless_zero.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Herbert Xu 2014-12-23 16:40:18 +11:00
parent 77584ee574
commit 15b66cd542
1 changed files with 11 additions and 3 deletions
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14
drivers/char/hw_random/core.c
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@ -105,7 +105,6 @@ static inline void cleanup_rng(struct kref *kref)
static void set_current_rng(struct hwrng *rng)
{
BUG_ON(!mutex_is_locked(&rng_mutex));
kref_get(&rng->ref);
current_rng = rng;
}
@ -150,6 +149,9 @@ static void put_rng(struct hwrng *rng)
static inline int hwrng_init(struct hwrng *rng)
{
if (kref_get_unless_zero(&rng->ref))
goto skip_init;
if (rng->init) {
int ret;
@ -157,6 +159,11 @@ static inline int hwrng_init(struct hwrng *rng)
if (ret)
return ret;
}
kref_init(&rng->ref);
reinit_completion(&rng->cleanup_done);
skip_init:
add_early_randomness(rng);
current_quality = rng->quality ? : default_quality;
@ -467,6 +474,9 @@ int hwrng_register(struct hwrng *rng)
goto out_unlock;
}
init_completion(&rng->cleanup_done);
complete(&rng->cleanup_done);
old_rng = current_rng;
err = 0;
if (!old_rng) {
@ -494,8 +504,6 @@ int hwrng_register(struct hwrng *rng)
add_early_randomness(rng);
}
init_completion(&rng->cleanup_done);
out_unlock:
mutex_unlock(&rng_mutex);
out: