[PATCH 5.5 114/367] crypto: api - Check spawn->alg under lock in crypto_drop_spawn

Greg Kroah-Hartman
2020-02-10T12:50:18Z

From: Herbert Xu <herbert@gondor.apana.org.au>

commit 7db3b61b6bba4310f454588c2ca6faf2958ad79f upstream.

We need to check whether spawn->alg is NULL under lock as otherwise
the algorithm could be removed from under us after we have checked
it and found it to be non-NULL. This could cause us to remove the
spawn from a non-existent list.

Fixes: 7ede5a5ba55a ("crypto: api - Fix crypto_drop_spawn crash...")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
crypto/algapi.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -669,11 +669,9 @@ EXPORT_SYMBOL_GPL(crypto_grab_spawn);

void crypto_drop_spawn(struct crypto_spawn *spawn)
{
- if (!spawn->alg)
- return;
-
down_write(&crypto_alg_sem);
- list_del(&spawn->list);
+ if (spawn->alg)
+ list_del(&spawn->list);
up_write(&crypto_alg_sem);
}
EXPORT_SYMBOL_GPL(crypto_drop_spawn);