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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Herbert Xu <herbert@gondor.apana.org.au>
Subject: [PATCH 4.9 030/116] crypto: api - Check spawn->alg under lock in crypto_drop_spawn
Date:   Thu, 13 Feb 2020 07:19:34 -0800
Message-Id: <20200213151854.692220564@linuxfoundation.org>
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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
@@ -652,11 +652,9 @@ 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);