crypto: authenc - fix key parsing

Fix incorrect validation of the key passed to "authenc" AEADs that allowed crashing the kernel via AF_ALG. The real fix is in patch 1, but two drivers had to be converted to use crypto_authenc_extractkeys() too.

Please note: for the bcm and ccree driver changes I haven't re-run the self-tests, as I don't have that hardware. Please do so if you can.

Eric Biggers (3):
crypto: authenc - fix parsing key with misaligned rta_len
crypto: bcm - convert to use crypto_authenc_extractkeys()
crypto: ccree - convert to use crypto_authenc_extractkeys()

 crypto/authenc.c               | 14 ++++++++---
 drivers/crypto/Kconfig         |  1 +
 drivers/crypto/bcm/cipher.c    | 44 ++++++++++------------------------
 drivers/crypto/ccree/cc_aead.c | 40 +++++++++++++++----------------
 4 files changed, 44 insertions(+), 55 deletions(-)

2.19.2

From: Eric Biggers <[email protected]>

Keys for "authenc" AEADs are formatted as an rtattr containing a 4-byte 'enckeylen', followed by an authentication key and an encryption key. crypto_authenc_extractkeys() parses the key to find the inner keys.

However, it fails to consider the case where the rtattr's payload is longer than 4 bytes but not 4-byte aligned, and where the key ends before the next 4-byte aligned boundary. In this case, 'keylen -= RTA_ALIGN(rta->rta_len);' underflows to a value near UINT_MAX. This causes a buffer overread and crash during crypto_ahash_setkey().

Fix it by restricting the rtattr payload to the expected size.

Reproducer using AF_ALG:

	#include <linux/if_alg.h>
	#include <linux/rtnetlink.h>
	#include <sys/socket.h>

	int main()
	{
		int fd;
		struct sockaddr_alg addr = {
			.salg_type = "aead",
			.salg_name = "authenc(hmac(sha256),cbc(aes))",
		};
		struct {
			struct rtattr attr;
			__be32 enckeylen;
			char keys[1];
		} __attribute__((packed)) key = {
			.attr.rta_len = sizeof(key),
			.attr.rta_type = 1 /* CRYPTO_AUTHENC_KEYA_PARAM */,
		};

		fd = socket(AF_ALG, SOCK_SEQPACKET, 0);
		bind(fd, (void *)&addr, sizeof(addr));
		setsockopt(fd, SOL_ALG, ALG_SET_KEY, &key, sizeof(key));
	}

It caused:

	BUG: unable to handle kernel paging request at ffff88007ffdc000
	PGD 2e01067 P4D 2e01067 PUD 2e04067 PMD 2e05067 PTE 0
	Oops: 0000 [#1] SMP
	CPU: 0 PID: 883 Comm: authenc Not tainted 4.20.0-rc1-00108-g00c9fe37a7f27 #13
	Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014
	RIP: 0010:sha256_ni_transform+0xb3/0x330 arch/x86/crypto/sha256_ni_asm.S:155
	[...]
	Call Trace:
	 sha256_ni_finup+0x10/0x20 arch/x86/crypto/sha256_ssse3_glue.c:321
	 crypto_shash_finup+0x1a/0x30 crypto/shash.c:178
	 shash_digest_unaligned+0x45/0x60 crypto/shash.c:186
	 crypto_shash_digest+0x24/0x40 crypto/shash.c:202
	 hmac_setkey+0x135/0x1e0 crypto/hmac.c:66
	 crypto_shash_setkey+0x2b/0xb0 crypto/shash.c:66
	 shash_async_setkey+0x10/0x20 crypto/shash.c:223
	 crypto_ahash_setkey+0x2d/0xa0 crypto/ahash.c:202
	 crypto_authenc_setkey+0x68/0x100 crypto/authenc.c:96
	 crypto_aead_setkey+0x2a/0xc0 crypto/aead.c:62
	 aead_setkey+0xc/0x10 crypto/algif_aead.c:526
	 alg_setkey crypto/af_alg.c:223 [inline]
	 alg_setsockopt+0xfe/0x130 crypto/af_alg.c:256
	 __sys_setsockopt+0x6d/0xd0 net/socket.c:1902
	 __do_sys_setsockopt net/socket.c:1913 [inline]
	 __se_sys_setsockopt net/socket.c:1910 [inline]
	 __x64_sys_setsockopt+0x1f/0x30 net/socket.c:1910
	 do_syscall_64+0x4a/0x180 arch/x86/entry/common.c:290
	 entry_SYSCALL_64_after_hwframe+0x49/0xbe

---
 crypto/authenc.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

index 37f54d1b2f669..4be293a4b5f0f 100644
@@ -58,14 +58,22 @@ int crypto_authenc_extractkeys(struct crypto_authenc_keys *keys, const u8 *key,
 		return -EINVAL;
 	if (rta->rta_type != CRYPTO_AUTHENC_KEYA_PARAM)
 		return -EINVAL;
-	if (RTA_PAYLOAD(rta) < sizeof(*param))
+
+	/*
+	 * RTA_OK() didn't align the rtattr's payload when validating that it
+	 * fits in the buffer.  Yet, the keys should start on the next 4-byte
+	 * aligned boundary.  To avoid confusion, require that the rtattr
+	 * payload be exactly the param struct, which has a 4-byte aligned size.
+	 */
+	if (RTA_PAYLOAD(rta) != sizeof(*param))
 		return -EINVAL;
+	BUILD_BUG_ON(sizeof(*param) % RTA_ALIGNTO);
 
 	param = RTA_DATA(rta);
 	keys->enckeylen = be32_to_cpu(param->enckeylen);
 
-	key += RTA_ALIGN(rta->rta_len);
-	keylen -= RTA_ALIGN(rta->rta_len);
+	key += rta->rta_len;
+	keylen -= rta->rta_len;
 
 	if (keylen < keys->enckeylen)
 		return -EINVAL;

2.19.2

From: Eric Biggers <[email protected]>

Convert the bcm crypto driver to use crypto_authenc_extractkeys() so that it picks up the fix for broken validation of rtattr::rta_len.

This also fixes the DES weak key check to actually be done on the right key. (It was checking the authentication key, not the encryption key...)

---
 drivers/crypto/Kconfig      |  1 +
 drivers/crypto/bcm/cipher.c | 44 +++++++++++--------------------------
 2 files changed, 14 insertions(+), 31 deletions(-)

index d80751d48cf1e..04ab0f5d272ee 100644
@@ -692,6 +692,7 @@ config CRYPTO_DEV_BCM_SPU
 	depends on ARCH_BCM_IPROC
 	depends on MAILBOX
 	default m
+	select CRYPTO_AUTHENC
 	select CRYPTO_DES
 	select CRYPTO_MD5
 	select CRYPTO_SHA1

2.19.2

From: Eric Biggers <[email protected]>

Convert the ccree crypto driver to use crypto_authenc_extractkeys() so that it picks up the fix for broken validation of rtattr::rta_len.

---
 drivers/crypto/ccree/cc_aead.c | 40 ++++++++++++++++------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

index f2643cda45db9..a3527c00b29a9 100644
@@ -549,13 +549,12 @@ static int cc_aead_setkey(struct crypto_aead *tfm, const u8 *key,
 			  unsigned int keylen)
 {
 	struct cc_aead_ctx *ctx = crypto_aead_ctx(tfm);
-	struct rtattr *rta = (struct rtattr *)key;
 	struct cc_crypto_req cc_req = {};
-	struct crypto_authenc_key_param *param;
 	struct cc_hw_desc desc[MAX_AEAD_SETKEY_SEQ];
-	int rc = -EINVAL;
 	unsigned int seq_len = 0;
 	struct device *dev = drvdata_to_dev(ctx->drvdata);
+	const u8 *enckey, *authkey;
+	int rc;
 
 	dev_dbg(dev, "Setting key in context @%p for %s. key=%p keylen=%u\n",
 		ctx, crypto_tfm_alg_name(crypto_aead_tfm(tfm)), key, keylen);

@@ -563,35 +562,33 @@ static int cc_aead_setkey(struct crypto_aead *tfm, const u8 *key,
 	/* STAT_PHASE_0: Init and sanity checks */
 
 	if (ctx->auth_mode != DRV_HASH_NULL) { /* authenc() alg. */
-		if (!RTA_OK(rta, keylen))
-			goto badkey;
-		if (rta->rta_type != CRYPTO_AUTHENC_KEYA_PARAM)
-			goto badkey;
-		if (RTA_PAYLOAD(rta) < sizeof(*param))
-			goto badkey;
-		param = RTA_DATA(rta);
-		ctx->enc_keylen = be32_to_cpu(param->enckeylen);
-		key += RTA_ALIGN(rta->rta_len);
-		keylen -= RTA_ALIGN(rta->rta_len);
-		if (keylen < ctx->enc_keylen)
+		struct crypto_authenc_keys keys;
+
+		rc = crypto_authenc_extractkeys(&keys, key, keylen);
+		if (rc)
 			goto badkey;
-		ctx->auth_keylen = keylen - ctx->enc_keylen;
+		enckey = keys.enckey;
+		authkey = keys.authkey;
+		ctx->enc_keylen = keys.enckeylen;
+		ctx->auth_keylen = keys.authkeylen;
 
 		if (ctx->cipher_mode == DRV_CIPHER_CTR) {
 			/* the nonce is stored in bytes at end of key */
+			rc = -EINVAL;
 			if (ctx->enc_keylen <
 			    (AES_MIN_KEY_SIZE + CTR_RFC3686_NONCE_SIZE))
 				goto badkey;
 			/* Copy nonce from last 4 bytes in CTR key to
 			 *  first 4 bytes in CTR IV
 			 */
-			memcpy(ctx->ctr_nonce, key + ctx->auth_keylen +
-			       ctx->enc_keylen - CTR_RFC3686_NONCE_SIZE,
-			       CTR_RFC3686_NONCE_SIZE);
+			memcpy(ctx->ctr_nonce, enckey + ctx->enc_keylen -
+			       CTR_RFC3686_NONCE_SIZE, CTR_RFC3686_NONCE_SIZE);
 			/* Set CTR key size */
 			ctx->enc_keylen -= CTR_RFC3686_NONCE_SIZE;
 		}
 	} else { /* non-authenc - has just one key */
+		enckey = key;
+		authkey = NULL;
 		ctx->enc_keylen = keylen;
 		ctx->auth_keylen = 0;
 	}

@@ -603,13 +600,14 @@ static int cc_aead_setkey(struct crypto_aead *tfm, const u8 *key,
 	/* STAT_PHASE_1: Copy key to ctx */
 
 	/* Get key material */
-	memcpy(ctx->enckey, key + ctx->auth_keylen, ctx->enc_keylen);
+	memcpy(ctx->enckey, enckey, ctx->enc_keylen);
 	if (ctx->enc_keylen == 24)
 		memset(ctx->enckey + 24, 0, CC_AES_KEY_SIZE_MAX - 24);
 	if (ctx->auth_mode == DRV_HASH_XCBC_MAC) {
-		memcpy(ctx->auth_state.xcbc.xcbc_keys, key, ctx->auth_keylen);
+		memcpy(ctx->auth_state.xcbc.xcbc_keys, authkey,
+		       ctx->auth_keylen);
 	} else if (ctx->auth_mode != DRV_HASH_NULL) { /* HMAC */
-		rc = cc_get_plain_hmac_key(tfm, key, ctx->auth_keylen);
+		rc = cc_get_plain_hmac_key(tfm, authkey, ctx->auth_keylen);
 		if (rc)
 			goto badkey;
 	}

2.19.2

All applied. Thanks.

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt