crypto: vmac - separate tfm and request context

syzbot reported a crash in vmac_final() when multiple threads
concurrently use the same "vmac(aes)" transform through AF_ALG.  The bug
is pretty fundamental: the VMAC template doesn't separate per-request
state from per-tfm (per-key) state like the other hash algorithms do,
but rather stores it all in the tfm context.  That's wrong.

Also, vmac_final() incorrectly zeroes most of the state including the
derived keys and cached pseudorandom pad.  Therefore, only the first
VMAC invocation with a given key calculates the correct digest.

Fix these bugs by splitting the per-tfm state from the per-request state
and using the proper init/update/final sequencing for requests.

Reproducer for the crash:

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

    int main()
    {
            int fd;
            struct sockaddr_alg addr = {
                    .salg_type = "hash",
                    .salg_name = "vmac(aes)",
            };
            char buf[256] = { 0 };

            fd = socket(AF_ALG, SOCK_SEQPACKET, 0);
            bind(fd, (void *)&addr, sizeof(addr));
            setsockopt(fd, SOL_ALG, ALG_SET_KEY, buf, 16);
            fork();
            fd = accept(fd, NULL, NULL);
            for (;;)
                    write(fd, buf, 256);
    }

The immediate cause of the crash is that vmac_ctx_t.partial_size exceeds
VMAC_NHBYTES, causing vmac_final() to memset() a negative length.

Reported-by: syzbot+264bca3a6e8d645550d3@syzkaller.appspotmail.com
Fixes: f1939f7c ("crypto: vmac - New hash algorithm for intel_txt support")
Cc: <stable@vger.kernel.org> # v2.6.32+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/vmac.h

-/*
- * Modified to interface to the Linux kernel
- * Copyright (c) 2009, Intel Corporation.
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms and conditions of the GNU General Public License,
- * version 2, as published by the Free Software Foundation.
- *
- * This program is distributed in the hope it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
- * more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
- * Place - Suite 330, Boston, MA 02111-1307 USA.
- */
-
-#ifndef __CRYPTO_VMAC_H
-#define __CRYPTO_VMAC_H
-
-/* --------------------------------------------------------------------------
- * VMAC and VHASH Implementation by Ted Krovetz (tdk@acm.org) and Wei Dai.
- * This implementation is herby placed in the public domain.
- * The authors offers no warranty. Use at your own risk.
- * Please send bug reports to the authors.
- * Last modified: 17 APR 08, 1700 PDT
- * ----------------------------------------------------------------------- */
-
-/*
- * User definable settings.
- */
-#define VMAC_TAG_LEN	64
-#define VMAC_KEY_SIZE	128/* Must be 128, 192 or 256			*/
-#define VMAC_KEY_LEN	(VMAC_KEY_SIZE/8)
-#define VMAC_NHBYTES	128/* Must 2^i for any 3 < i < 13 Standard = 128*/
-
-/*
- * This implementation uses u32 and u64 as names for unsigned 32-
- * and 64-bit integer types. These are defined in C99 stdint.h. The
- * following may need adaptation if you are not running a C99 or
- * Microsoft C environment.
- */
-struct vmac_ctx {
-	u64 nhkey[(VMAC_NHBYTES/8)+2*(VMAC_TAG_LEN/64-1)];
-	u64 polykey[2*VMAC_TAG_LEN/64];
-	u64 l3key[2*VMAC_TAG_LEN/64];
-	u64 polytmp[2*VMAC_TAG_LEN/64];
-	u64 cached_nonce[2];
-	u64 cached_aes[2];
-	int first_block_processed;
-};
-
-typedef u64 vmac_t;
-
-struct vmac_ctx_t {
-	struct crypto_cipher *child;
-	struct vmac_ctx __vmac_ctx;
-	u8 partial[VMAC_NHBYTES];	/* partial block */
-	int partial_size;		/* size of the partial block */
-};
-
-#endif /* __CRYPTO_VMAC_H */