[PATCH 3.16 17/99] crypto: api - Check spawn->alg under lock in crypto_drop_spawn

[Ben Hutchings]

3.16.84-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

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...")
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 crypto/algapi.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -618,11 +618,9 @@ EXPORT_SYMBOL_GPL(crypto_init_spawn2);
 
 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);