linux-kernel - [PATCH 1/4] crypto: introduce CRYPTO_ALG_ALLOCATES

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Date:   Tue, 16 Jun 2020 11:01:31 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
cc:     "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, Mike Snitzer <msnitzer@...hat.com>,
        Milan Broz <mbroz@...hat.com>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] crypto: introduce CRYPTO_ALG_ALLOCATES_MEMORY

Introduce a new flag CRYPTO_ALG_ALLOCATES_MEMORY and modify dm-crypt, so
that it uses only drivers without this flag.

If the flag is set, then the crypto driver allocates memory in its request
routine. Such drivers are not suitable for disk encryption because
GFP_ATOMIC allocation can fail anytime (causing random I/O errors) and
GFP_KERNEL allocation can recurse into the block layer, causing a
deadlock.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

Index: linux-2.6/include/linux/crypto.h
===================================================================
--- linux-2.6.orig/include/linux/crypto.h
+++ linux-2.6/include/linux/crypto.h
@@ -97,9 +97,15 @@
 #define CRYPTO_ALG_OPTIONAL_KEY		0x00004000
 
 /*
+ * The driver is allocating emmory in its encrypt or decrypt callback,
+ * so it should not be used to encrypt block devices.
+ */
+#define CRYPTO_ALG_ALLOCATES_MEMORY	0x00008000
+
+/*
  * Don't trigger module loading
  */
-#define CRYPTO_NOLOAD			0x00008000
+#define CRYPTO_NOLOAD			0x00010000
 
 /*
  * Transform masks and values (for crt_flags).
Index: linux-2.6/drivers/md/dm-crypt.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-crypt.c
+++ linux-2.6/drivers/md/dm-crypt.c
@@ -419,7 +419,7 @@ static int crypt_iv_lmk_ctr(struct crypt
 		return -EINVAL;
 	}
 
-	lmk->hash_tfm = crypto_alloc_shash("md5", 0, 0);
+	lmk->hash_tfm = crypto_alloc_shash("md5", 0, CRYPTO_ALG_ALLOCATES_MEMORY);
 	if (IS_ERR(lmk->hash_tfm)) {
 		ti->error = "Error initializing LMK hash";
 		return PTR_ERR(lmk->hash_tfm);
@@ -581,7 +581,7 @@ static int crypt_iv_tcw_ctr(struct crypt
 		return -EINVAL;
 	}
 
-	tcw->crc32_tfm = crypto_alloc_shash("crc32", 0, 0);
+	tcw->crc32_tfm = crypto_alloc_shash("crc32", 0, CRYPTO_ALG_ALLOCATES_MEMORY);
 	if (IS_ERR(tcw->crc32_tfm)) {
 		ti->error = "Error initializing CRC32 in TCW";
 		return PTR_ERR(tcw->crc32_tfm);
@@ -768,7 +768,7 @@ static int crypt_iv_elephant_ctr(struct
 	struct iv_elephant_private *elephant = &cc->iv_gen_private.elephant;
 	int r;
 
-	elephant->tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
+	elephant->tfm = crypto_alloc_skcipher("ecb(aes)", 0, CRYPTO_ALG_ALLOCATES_MEMORY);
 	if (IS_ERR(elephant->tfm)) {
 		r = PTR_ERR(elephant->tfm);
 		elephant->tfm = NULL;
@@ -2088,7 +2088,7 @@ static int crypt_alloc_tfms_skcipher(str
 		return -ENOMEM;
 
 	for (i = 0; i < cc->tfms_count; i++) {
-		cc->cipher_tfm.tfms[i] = crypto_alloc_skcipher(ciphermode, 0, 0);
+		cc->cipher_tfm.tfms[i] = crypto_alloc_skcipher(ciphermode, 0, CRYPTO_ALG_ALLOCATES_MEMORY);
 		if (IS_ERR(cc->cipher_tfm.tfms[i])) {
 			err = PTR_ERR(cc->cipher_tfm.tfms[i]);
 			crypt_free_tfms(cc);
@@ -2114,7 +2114,7 @@ static int crypt_alloc_tfms_aead(struct
 	if (!cc->cipher_tfm.tfms)
 		return -ENOMEM;
 
-	cc->cipher_tfm.tfms_aead[0] = crypto_alloc_aead(ciphermode, 0, 0);
+	cc->cipher_tfm.tfms_aead[0] = crypto_alloc_aead(ciphermode, 0, CRYPTO_ALG_ALLOCATES_MEMORY);
 	if (IS_ERR(cc->cipher_tfm.tfms_aead[0])) {
 		err = PTR_ERR(cc->cipher_tfm.tfms_aead[0]);
 		crypt_free_tfms(cc);
@@ -2565,7 +2565,7 @@ static int crypt_ctr_auth_cipher(struct
 		return -ENOMEM;
 	strncpy(mac_alg, start, end - start);
 
-	mac = crypto_alloc_ahash(mac_alg, 0, 0);
+	mac = crypto_alloc_ahash(mac_alg, 0, CRYPTO_ALG_ALLOCATES_MEMORY);
 	kfree(mac_alg);
 
 	if (IS_ERR(mac))