Commit message: crypto: hmac - require that the underlying hash algorithm is unkeyed

Because the HMAC template didn't check that its underlying hash
algorithm is unkeyed, trying to use "hmac(hmac(sha3-512-generic))"
through AF_ALG or through KEYCTL_DH_COMPUTE resulted in the inner HMAC
being used without having been keyed, resulting in sha3_update() being
called without sha3_init(), causing a stack buffer overflow.

This is a very old bug, but it seems to have only started causing real
problems when SHA-3 support was added (requires CONFIG_CRYPTO_SHA3)
because the innermost hash's state is ->import()ed from a zeroed buffer,
and it just so happens that other hash algorithms are fine with that,
but SHA-3 is not.  However, there could be arch or hardware-dependent
hash algorithms also affected; I couldn't test everything.

Fix the bug by introducing a function crypto_shash_alg_has_setkey()
which tests whether a shash algorithm is keyed.  Then update the HMAC
template to require that its underlying hash algorithm is unkeyed.

Here is a reproducer:

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

    int main()
    {
        int algfd;
        struct sockaddr_alg addr = {
            .salg_type = "hash",
            .salg_name = "hmac(hmac(sha3-512-generic))",
        };
        char key[4096] = { 0 };

        algfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
        bind(algfd, (const struct sockaddr *)&addr, sizeof(addr));
        setsockopt(algfd, SOL_ALG, ALG_SET_KEY, key, sizeof(key));
    }

Here was the KASAN report from syzbot:

    BUG: KASAN: stack-out-of-bounds in memcpy include/linux/string.h:341  [inline]
    BUG: KASAN: stack-out-of-bounds in sha3_update+0xdf/0x2e0  crypto/sha3_generic.c:161
    Write of size 4096 at addr ffff8801cca07c40 by task syzkaller076574/3044

    CPU: 1 PID: 3044 Comm: syzkaller076574 Not tainted 4.14.0-mm1+ #25
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  Google 01/01/2011
    Call Trace:
      __dump_stack lib/dump_stack.c:17 [inline]
      dump_stack+0x194/0x257 lib/dump_stack.c:53
      print_address_description+0x73/0x250 mm/kasan/report.c:252
      kasan_report_error mm/kasan/report.c:351 [inline]
      kasan_report+0x25b/0x340 mm/kasan/report.c:409
      check_memory_region_inline mm/kasan/kasan.c:260 [inline]
      check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
      memcpy+0x37/0x50 mm/kasan/kasan.c:303
      memcpy include/linux/string.h:341 [inline]
      sha3_update+0xdf/0x2e0 crypto/sha3_generic.c:161
      crypto_shash_update+0xcb/0x220 crypto/shash.c:109
      shash_finup_unaligned+0x2a/0x60 crypto/shash.c:151
      crypto_shash_finup+0xc4/0x120 crypto/shash.c:165
      hmac_finup+0x182/0x330 crypto/hmac.c:152
      crypto_shash_finup+0xc4/0x120 crypto/shash.c:165
      shash_digest_unaligned+0x9e/0xd0 crypto/shash.c:172
      crypto_shash_digest+0xc4/0x120 crypto/shash.c:186
      hmac_setkey+0x36a/0x690 crypto/hmac.c:66
      crypto_shash_setkey+0xad/0x190 crypto/shash.c:64
      shash_async_setkey+0x47/0x60 crypto/shash.c:207
      crypto_ahash_setkey+0xaf/0x180 crypto/ahash.c:200
      hash_setkey+0x40/0x90 crypto/algif_hash.c:446
      alg_setkey crypto/af_alg.c:221 [inline]
      alg_setsockopt+0x2a1/0x350 crypto/af_alg.c:254
      SYSC_setsockopt net/socket.c:1851 [inline]
      SyS_setsockopt+0x189/0x360 net/socket.c:1830
      entry_SYSCALL_64_fastpath+0x1f/0x96

Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
CVE: CVE-2017-17806
CWE: CWE-787
Vulnerability description: The HMAC implementation (crypto/hmac.c) in the Linux kernel before 4.14.8 does not validate that the underlying cryptographic hash algorithm is unkeyed, allowing a local attacker able to use the AF_ALG-based hash interface (CONFIG_CRYPTO_USER_API_HASH) and the SHA-3 hash algorithm (CONFIG_CRYPTO_SHA3) to cause a kernel stack buffer overflow by executing a crafted sequence of system calls that encounter a missing SHA-3 initialization.

Project: linux
File: hmac.c

static int hmac_setkey(struct crypto_shash *parent,
		       const u8 *inkey, unsigned int keylen)
{
	int bs = crypto_shash_blocksize(parent);
	int ds = crypto_shash_digestsize(parent);
	int ss = crypto_shash_statesize(parent);
	char *ipad = crypto_shash_ctx_aligned(parent);
	char *opad = ipad + ss;
	struct hmac_ctx *ctx = align_ptr(opad + ss,
					 crypto_tfm_ctx_alignment());
	struct crypto_shash *hash = ctx->hash;
	SHASH_DESC_ON_STACK(shash, hash);
	unsigned int i;

	shash->tfm = hash;
	shash->flags = crypto_shash_get_flags(parent)
		& CRYPTO_TFM_REQ_MAY_SLEEP;

	if (keylen > bs) {
		int err;

		err = crypto_shash_digest(shash, inkey, keylen, ipad);
		if (err)
			return err;

		keylen = ds;
	} else
		memcpy(ipad, inkey, keylen);

	memset(ipad + keylen, 0, bs - keylen);
	memcpy(opad, ipad, bs);

	for (i = 0; i < bs; i++) {
		ipad[i] ^= HMAC_IPAD_VALUE;
		opad[i] ^= HMAC_OPAD_VALUE;
	}

	return crypto_shash_init(shash) ?:
	       crypto_shash_update(shash, ipad, bs) ?:
	       crypto_shash_export(shash, ipad) ?:
	       crypto_shash_init(shash) ?:
	       crypto_shash_update(shash, opad, bs) ?:
	       crypto_shash_export(shash, opad);
}

Project: linux
File: shash.c

int crypto_init_shash_ops_async(struct crypto_tfm *tfm)
{
	struct crypto_alg *calg = tfm->__crt_alg;
	struct shash_alg *alg = __crypto_shash_alg(calg);
	struct crypto_ahash *crt = __crypto_ahash_cast(tfm);
	struct crypto_shash **ctx = crypto_tfm_ctx(tfm);
	struct crypto_shash *shash;

	if (!crypto_mod_get(calg))
		return -EAGAIN;

	shash = crypto_create_tfm(calg, &crypto_shash_type);
	if (IS_ERR(shash)) {
		crypto_mod_put(calg);
		return PTR_ERR(shash);
	}

	*ctx = shash;
	tfm->exit = crypto_exit_shash_ops_async;

	crt->init = shash_async_init;
	crt->update = shash_async_update;
	crt->final = shash_async_final;
	crt->finup = shash_async_finup;
	crt->digest = shash_async_digest;
	crt->setkey = shash_async_setkey;

	crt->has_setkey = alg->setkey != shash_no_setkey;

	if (alg->export)
		crt->export = shash_async_export;
	if (alg->import)
		crt->import = shash_async_import;

	crt->reqsize = sizeof(struct shash_desc) + crypto_shash_descsize(shash);

	return 0;
}

Project: linux
File: shash.c

static int crypto_shash_report(struct sk_buff *skb, struct crypto_alg *alg)
{
	struct crypto_report_hash rhash;
	struct shash_alg *salg = __crypto_shash_alg(alg);

	strncpy(rhash.type, "shash", sizeof(rhash.type));

	rhash.blocksize = alg->cra_blocksize;
	rhash.digestsize = salg->digestsize;

	if (nla_put(skb, CRYPTOCFGA_REPORT_HASH,
		    sizeof(struct crypto_report_hash), &rhash))
		goto nla_put_failure;
	return 0;

nla_put_failure:
	return -EMSGSIZE;
}

Project: linux
File: shash.c

int shash_ahash_digest(struct ahash_request *req, struct shash_desc *desc)
{
	unsigned int nbytes = req->nbytes;
	struct scatterlist *sg;
	unsigned int offset;
	int err;

	if (nbytes &&
	    (sg = req->src, offset = sg->offset,
	     nbytes < min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset))) {
		void *data;

		data = kmap_atomic(sg_page(sg));
		err = crypto_shash_digest(desc, data + offset, nbytes,
					  req->result);
		kunmap_atomic(data);
		crypto_yield(desc->flags);
	} else
		err = crypto_shash_init(desc) ?:
		      shash_ahash_finup(req, desc);

	return err;
}

Project: linux
File: shash.c

static inline unsigned int shash_align_buffer_size(unsigned len,
						   unsigned long mask)
{
	typedef u8 __aligned_largest u8_aligned;
	return len + (mask & ~(__alignof__(u8_aligned) - 1));
}

Project: linux
File: shash.c

static int shash_final_unaligned(struct shash_desc *desc, u8 *out)
{
	struct crypto_shash *tfm = desc->tfm;
	unsigned long alignmask = crypto_shash_alignmask(tfm);
	struct shash_alg *shash = crypto_shash_alg(tfm);
	unsigned int ds = crypto_shash_digestsize(tfm);
	u8 ubuf[shash_align_buffer_size(ds, alignmask)]
		__aligned_largest;
	u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);
	int err;

	err = shash->final(desc, buf);
	if (err)
		goto out;

	memcpy(out, buf, ds);

out:
	memset(buf, 0, ds);
	return err;
}

Project: linux
File: shash.c

 static int shash_setkey_unaligned(struct crypto_shash *tfm, const u8 *key,
 				  unsigned int keylen)
{
	struct shash_alg *shash = crypto_shash_alg(tfm);
	unsigned long alignmask = crypto_shash_alignmask(tfm);
	unsigned long absize;
	u8 *buffer, *alignbuffer;
	int err;

	absize = keylen + (alignmask & ~(crypto_tfm_ctx_alignment() - 1));
	buffer = kmalloc(absize, GFP_ATOMIC);
	if (!buffer)
		return -ENOMEM;

	alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
	memcpy(alignbuffer, key, keylen);
	err = shash->setkey(tfm, alignbuffer, keylen);
	kzfree(buffer);
	return err;
}

Project: linux
File: shash.c

static int shash_update_unaligned(struct shash_desc *desc, const u8 *data,
				  unsigned int len)
{
	struct crypto_shash *tfm = desc->tfm;
	struct shash_alg *shash = crypto_shash_alg(tfm);
	unsigned long alignmask = crypto_shash_alignmask(tfm);
	unsigned int unaligned_len = alignmask + 1 -
				     ((unsigned long)data & alignmask);
	u8 ubuf[shash_align_buffer_size(unaligned_len, alignmask)]
		__aligned_largest;
	u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);
	int err;

	if (unaligned_len > len)
		unaligned_len = len;

	memcpy(buf, data, unaligned_len);
	err = shash->update(desc, buf, unaligned_len);
	memset(buf, 0, unaligned_len);

	return err ?:
	       shash->update(desc, data + unaligned_len, len - unaligned_len);
}