From b32a7dc8aef1882fbf983eb354837488cc9d54dc Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Mon, 27 Nov 2017 23:23:05 -0800
Subject: [PATCH] crypto: algif_aead - fix reference counting of null skcipher
Git-commit: b32a7dc8aef1882fbf983eb354837488cc9d54dc
Patch-mainline: v4.15-rc4
References: bsc#1154737

In the AEAD interface for AF_ALG, the reference to the "null skcipher"
held by each tfm was being dropped in the wrong place -- when each
af_alg_ctx was freed instead of when the aead_tfm was freed.  As
discovered by syzkaller, a specially crafted program could use this to
cause the null skcipher to be freed while it is still in use.

Fix it by dropping the reference in the right place.

Fixes: 72548b093ee3 ("crypto: algif_aead - copy AAD from src to dst")
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 crypto/algif_aead.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/algif_aead.c b/crypto/algif_aead.c
index aacae0837aff..9d73be28cf01 100644
--- a/crypto/algif_aead.c
+++ b/crypto/algif_aead.c
@@ -487,6 +487,7 @@ static void aead_release(void *private)
 	struct aead_tfm *tfm = private;
 
 	crypto_free_aead(tfm->aead);
+	crypto_put_default_null_skcipher2();
 	kfree(tfm);
 }
 
@@ -519,7 +520,6 @@ static void aead_sock_destruct(struct sock *sk)
 	unsigned int ivlen = crypto_aead_ivsize(tfm);
 
 	af_alg_pull_tsgl(sk, ctx->used, NULL, 0);
-	crypto_put_default_null_skcipher2();
 	sock_kzfree_s(sk, ctx->iv, ivlen);
 	sock_kfree_s(sk, ctx, ctx->len);
 	af_alg_release_parent(sk);
-- 
2.16.4