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![Eric Biggers](/assets/img/avatar_default.png)
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>
276 lines
6.9 KiB
C
276 lines
6.9 KiB
C
/*
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* Cryptographic API.
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*
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* HMAC: Keyed-Hashing for Message Authentication (RFC2104).
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*
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* Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
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* Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
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*
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* The HMAC implementation is derived from USAGI.
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* Copyright (c) 2002 Kazunori Miyazawa <miyazawa@linux-ipv6.org> / USAGI
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the Free
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* Software Foundation; either version 2 of the License, or (at your option)
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* any later version.
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*
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*/
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#include <crypto/hmac.h>
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#include <crypto/internal/hash.h>
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#include <crypto/scatterwalk.h>
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#include <linux/err.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/scatterlist.h>
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#include <linux/string.h>
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struct hmac_ctx {
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struct crypto_shash *hash;
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};
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static inline void *align_ptr(void *p, unsigned int align)
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{
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return (void *)ALIGN((unsigned long)p, align);
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}
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static inline struct hmac_ctx *hmac_ctx(struct crypto_shash *tfm)
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{
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return align_ptr(crypto_shash_ctx_aligned(tfm) +
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crypto_shash_statesize(tfm) * 2,
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crypto_tfm_ctx_alignment());
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}
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static int hmac_setkey(struct crypto_shash *parent,
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const u8 *inkey, unsigned int keylen)
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{
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int bs = crypto_shash_blocksize(parent);
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int ds = crypto_shash_digestsize(parent);
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int ss = crypto_shash_statesize(parent);
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char *ipad = crypto_shash_ctx_aligned(parent);
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char *opad = ipad + ss;
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struct hmac_ctx *ctx = align_ptr(opad + ss,
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crypto_tfm_ctx_alignment());
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struct crypto_shash *hash = ctx->hash;
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SHASH_DESC_ON_STACK(shash, hash);
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unsigned int i;
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shash->tfm = hash;
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shash->flags = crypto_shash_get_flags(parent)
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& CRYPTO_TFM_REQ_MAY_SLEEP;
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if (keylen > bs) {
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int err;
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err = crypto_shash_digest(shash, inkey, keylen, ipad);
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if (err)
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return err;
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keylen = ds;
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} else
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memcpy(ipad, inkey, keylen);
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memset(ipad + keylen, 0, bs - keylen);
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memcpy(opad, ipad, bs);
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for (i = 0; i < bs; i++) {
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ipad[i] ^= HMAC_IPAD_VALUE;
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opad[i] ^= HMAC_OPAD_VALUE;
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}
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return crypto_shash_init(shash) ?:
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crypto_shash_update(shash, ipad, bs) ?:
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crypto_shash_export(shash, ipad) ?:
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crypto_shash_init(shash) ?:
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crypto_shash_update(shash, opad, bs) ?:
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crypto_shash_export(shash, opad);
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}
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static int hmac_export(struct shash_desc *pdesc, void *out)
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{
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struct shash_desc *desc = shash_desc_ctx(pdesc);
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desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
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return crypto_shash_export(desc, out);
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}
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static int hmac_import(struct shash_desc *pdesc, const void *in)
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{
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struct shash_desc *desc = shash_desc_ctx(pdesc);
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struct hmac_ctx *ctx = hmac_ctx(pdesc->tfm);
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desc->tfm = ctx->hash;
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desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
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return crypto_shash_import(desc, in);
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}
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static int hmac_init(struct shash_desc *pdesc)
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{
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return hmac_import(pdesc, crypto_shash_ctx_aligned(pdesc->tfm));
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}
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static int hmac_update(struct shash_desc *pdesc,
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const u8 *data, unsigned int nbytes)
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{
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struct shash_desc *desc = shash_desc_ctx(pdesc);
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desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
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return crypto_shash_update(desc, data, nbytes);
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}
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static int hmac_final(struct shash_desc *pdesc, u8 *out)
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{
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struct crypto_shash *parent = pdesc->tfm;
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int ds = crypto_shash_digestsize(parent);
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int ss = crypto_shash_statesize(parent);
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char *opad = crypto_shash_ctx_aligned(parent) + ss;
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struct shash_desc *desc = shash_desc_ctx(pdesc);
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desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
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return crypto_shash_final(desc, out) ?:
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crypto_shash_import(desc, opad) ?:
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crypto_shash_finup(desc, out, ds, out);
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}
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static int hmac_finup(struct shash_desc *pdesc, const u8 *data,
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unsigned int nbytes, u8 *out)
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{
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struct crypto_shash *parent = pdesc->tfm;
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int ds = crypto_shash_digestsize(parent);
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int ss = crypto_shash_statesize(parent);
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char *opad = crypto_shash_ctx_aligned(parent) + ss;
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struct shash_desc *desc = shash_desc_ctx(pdesc);
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desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
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return crypto_shash_finup(desc, data, nbytes, out) ?:
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crypto_shash_import(desc, opad) ?:
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crypto_shash_finup(desc, out, ds, out);
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}
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static int hmac_init_tfm(struct crypto_tfm *tfm)
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{
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struct crypto_shash *parent = __crypto_shash_cast(tfm);
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struct crypto_shash *hash;
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struct crypto_instance *inst = (void *)tfm->__crt_alg;
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struct crypto_shash_spawn *spawn = crypto_instance_ctx(inst);
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struct hmac_ctx *ctx = hmac_ctx(parent);
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hash = crypto_spawn_shash(spawn);
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if (IS_ERR(hash))
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return PTR_ERR(hash);
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parent->descsize = sizeof(struct shash_desc) +
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crypto_shash_descsize(hash);
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ctx->hash = hash;
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return 0;
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}
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static void hmac_exit_tfm(struct crypto_tfm *tfm)
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{
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struct hmac_ctx *ctx = hmac_ctx(__crypto_shash_cast(tfm));
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crypto_free_shash(ctx->hash);
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}
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static int hmac_create(struct crypto_template *tmpl, struct rtattr **tb)
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{
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struct shash_instance *inst;
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struct crypto_alg *alg;
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struct shash_alg *salg;
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int err;
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int ds;
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int ss;
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err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH);
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if (err)
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return err;
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salg = shash_attr_alg(tb[1], 0, 0);
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if (IS_ERR(salg))
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return PTR_ERR(salg);
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alg = &salg->base;
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/* The underlying hash algorithm must be unkeyed */
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err = -EINVAL;
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if (crypto_shash_alg_has_setkey(salg))
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goto out_put_alg;
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ds = salg->digestsize;
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ss = salg->statesize;
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if (ds > alg->cra_blocksize ||
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ss < alg->cra_blocksize)
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goto out_put_alg;
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inst = shash_alloc_instance("hmac", alg);
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err = PTR_ERR(inst);
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if (IS_ERR(inst))
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goto out_put_alg;
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err = crypto_init_shash_spawn(shash_instance_ctx(inst), salg,
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shash_crypto_instance(inst));
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if (err)
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goto out_free_inst;
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inst->alg.base.cra_priority = alg->cra_priority;
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inst->alg.base.cra_blocksize = alg->cra_blocksize;
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inst->alg.base.cra_alignmask = alg->cra_alignmask;
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ss = ALIGN(ss, alg->cra_alignmask + 1);
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inst->alg.digestsize = ds;
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inst->alg.statesize = ss;
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inst->alg.base.cra_ctxsize = sizeof(struct hmac_ctx) +
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ALIGN(ss * 2, crypto_tfm_ctx_alignment());
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inst->alg.base.cra_init = hmac_init_tfm;
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inst->alg.base.cra_exit = hmac_exit_tfm;
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inst->alg.init = hmac_init;
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inst->alg.update = hmac_update;
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inst->alg.final = hmac_final;
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inst->alg.finup = hmac_finup;
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inst->alg.export = hmac_export;
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inst->alg.import = hmac_import;
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inst->alg.setkey = hmac_setkey;
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err = shash_register_instance(tmpl, inst);
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if (err) {
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out_free_inst:
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shash_free_instance(shash_crypto_instance(inst));
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}
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out_put_alg:
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crypto_mod_put(alg);
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return err;
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}
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static struct crypto_template hmac_tmpl = {
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.name = "hmac",
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.create = hmac_create,
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.free = shash_free_instance,
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.module = THIS_MODULE,
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};
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static int __init hmac_module_init(void)
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{
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return crypto_register_template(&hmac_tmpl);
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}
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static void __exit hmac_module_exit(void)
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{
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crypto_unregister_template(&hmac_tmpl);
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}
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module_init(hmac_module_init);
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module_exit(hmac_module_exit);
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("HMAC hash algorithm");
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MODULE_ALIAS_CRYPTO("hmac");
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