[PATCH 2/3] crypto: skcipher - set CRYPTO_TFM_NEED_KEY if ->setkey() fails

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

Some algorithms have a ->setkey() method that is not atomic, in the
sense that setting a key can fail after changes were already made to the
tfm context.  In this case, if a key was already set the tfm can end up
in a state that corresponds to neither the old key nor the new key.

For example, in lrw.c, if gf128mul_init_64k_bbe() fails due to lack of
memory, then priv::table will be left NULL.  After that, encryption with
that tfm will cause a NULL pointer dereference.

It's not feasible to make all ->setkey() methods atomic, especially ones
that have to key multiple sub-tfms.  Therefore, make the crypto API set
CRYPTO_TFM_NEED_KEY if ->setkey() fails and the algorithm requires a
key, to prevent the tfm from being used until a new key is set.

[Cc stable mainly because when introducing the NEED_KEY flag I changed
 AF_ALG to rely on it; and unlike in-kernel crypto API users, AF_ALG
 previously didn't have this problem.  So these "incompletely keyed"
 states became theoretically accessible via AF_ALG -- though, the
 opportunities for causing real mischief seem pretty limited.]

Fixes: f8d33fac8480 ("crypto: skcipher - prevent using skciphers without setting key")
Cc: <stable@vger.kernel.org> # v4.16+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/skcipher.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index 2a969296bc248..de09ff60991e2 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -585,6 +585,12 @@ static unsigned int crypto_skcipher_extsize(struct crypto_alg *alg)
 	return crypto_alg_extsize(alg);
 }
 
+static void skcipher_set_needkey(struct crypto_skcipher *tfm)
+{
+	if (tfm->keysize)
+		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_NEED_KEY);
+}
+
 static int skcipher_setkey_blkcipher(struct crypto_skcipher *tfm,
 				     const u8 *key, unsigned int keylen)
 {
@@ -598,8 +604,10 @@ static int skcipher_setkey_blkcipher(struct crypto_skcipher *tfm,
 	err = crypto_blkcipher_setkey(blkcipher, key, keylen);
 	crypto_skcipher_set_flags(tfm, crypto_blkcipher_get_flags(blkcipher) &
 				       CRYPTO_TFM_RES_MASK);
-	if (err)
+	if (unlikely(err)) {
+		skcipher_set_needkey(tfm);
 		return err;
+	}
 
 	crypto_skcipher_clear_flags(tfm, CRYPTO_TFM_NEED_KEY);
 	return 0;
@@ -677,8 +685,7 @@ static int crypto_init_skcipher_ops_blkcipher(struct crypto_tfm *tfm)
 	skcipher->ivsize = crypto_blkcipher_ivsize(blkcipher);
 	skcipher->keysize = calg->cra_blkcipher.max_keysize;
 
-	if (skcipher->keysize)
-		crypto_skcipher_set_flags(skcipher, CRYPTO_TFM_NEED_KEY);
+	skcipher_set_needkey(skcipher);
 
 	return 0;
 }
@@ -698,8 +705,10 @@ static int skcipher_setkey_ablkcipher(struct crypto_skcipher *tfm,
 	crypto_skcipher_set_flags(tfm,
 				  crypto_ablkcipher_get_flags(ablkcipher) &
 				  CRYPTO_TFM_RES_MASK);
-	if (err)
+	if (unlikely(err)) {
+		skcipher_set_needkey(tfm);
 		return err;
+	}
 
 	crypto_skcipher_clear_flags(tfm, CRYPTO_TFM_NEED_KEY);
 	return 0;
@@ -776,8 +785,7 @@ static int crypto_init_skcipher_ops_ablkcipher(struct crypto_tfm *tfm)
 			    sizeof(struct ablkcipher_request);
 	skcipher->keysize = calg->cra_ablkcipher.max_keysize;
 
-	if (skcipher->keysize)
-		crypto_skcipher_set_flags(skcipher, CRYPTO_TFM_NEED_KEY);
+	skcipher_set_needkey(skcipher);
 
 	return 0;
 }
@@ -820,8 +828,10 @@ static int skcipher_setkey(struct crypto_skcipher *tfm, const u8 *key,
 	else
 		err = cipher->setkey(tfm, key, keylen);
 
-	if (err)
+	if (unlikely(err)) {
+		skcipher_set_needkey(tfm);
 		return err;
+	}
 
 	crypto_skcipher_clear_flags(tfm, CRYPTO_TFM_NEED_KEY);
 	return 0;
@@ -852,8 +862,7 @@ static int crypto_skcipher_init_tfm(struct crypto_tfm *tfm)
 	skcipher->ivsize = alg->ivsize;
 	skcipher->keysize = alg->max_keysize;
 
-	if (skcipher->keysize)
-		crypto_skcipher_set_flags(skcipher, CRYPTO_TFM_NEED_KEY);
+	skcipher_set_needkey(skcipher);
 
 	if (alg->exit)
 		skcipher->base.exit = crypto_skcipher_exit_tfm;
-- 
2.20.1