APPLIED[T]: [SRU][Trusty][Artful][PATCH 1/1] crypto: hmac - require that the underlying hash algorithm is unkeyed
Stefan Bader
stefan.bader at canonical.com
Fri Feb 2 10:00:25 UTC 2018
On 01.02.2018 17:06, Kleber Sacilotto de Souza wrote:
> From: Eric Biggers <ebiggers at google.com>
>
> 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 at googlegroups.com>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Eric Biggers <ebiggers at google.com>
> Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
>
> CVE-2017-17806
> (cherry picked from commit af3ff8045bbf3e32f1a448542e73abb4c8ceb6f1)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> ---
> crypto/hmac.c | 6 +++++-
> crypto/shash.c | 5 +++--
> include/crypto/internal/hash.h | 8 ++++++++
> 3 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/crypto/hmac.c b/crypto/hmac.c
> index ade790b454e9..758688b4bc6b 100644
> --- a/crypto/hmac.c
> +++ b/crypto/hmac.c
> @@ -197,11 +197,15 @@ static int hmac_create(struct crypto_template *tmpl, struct rtattr **tb)
> salg = shash_attr_alg(tb[1], 0, 0);
> if (IS_ERR(salg))
> return PTR_ERR(salg);
> + alg = &salg->base;
>
> + /* The underlying hash algorithm must be unkeyed */
> err = -EINVAL;
> + if (crypto_shash_alg_has_setkey(salg))
> + goto out_put_alg;
> +
> ds = salg->digestsize;
> ss = salg->statesize;
> - alg = &salg->base;
> if (ds > alg->cra_blocksize ||
> ss < alg->cra_blocksize)
> goto out_put_alg;
> diff --git a/crypto/shash.c b/crypto/shash.c
> index ac4d76350d1b..956979787efb 100644
> --- a/crypto/shash.c
> +++ b/crypto/shash.c
> @@ -24,11 +24,12 @@
>
> static const struct crypto_type crypto_shash_type;
>
> -static int shash_no_setkey(struct crypto_shash *tfm, const u8 *key,
> - unsigned int keylen)
> +int shash_no_setkey(struct crypto_shash *tfm, const u8 *key,
> + unsigned int keylen)
> {
> return -ENOSYS;
> }
> +EXPORT_SYMBOL_GPL(shash_no_setkey);
>
> static int shash_setkey_unaligned(struct crypto_shash *tfm, const u8 *key,
> unsigned int keylen)
> diff --git a/include/crypto/internal/hash.h b/include/crypto/internal/hash.h
> index 821eae8cbd8c..0af57a99c6a1 100644
> --- a/include/crypto/internal/hash.h
> +++ b/include/crypto/internal/hash.h
> @@ -70,6 +70,14 @@ int ahash_register_instance(struct crypto_template *tmpl,
> struct ahash_instance *inst);
> void ahash_free_instance(struct crypto_instance *inst);
>
> +int shash_no_setkey(struct crypto_shash *tfm, const u8 *key,
> + unsigned int keylen);
> +
> +static inline bool crypto_shash_alg_has_setkey(struct shash_alg *alg)
> +{
> + return alg->setkey != shash_no_setkey;
> +}
> +
> int crypto_init_ahash_spawn(struct crypto_ahash_spawn *spawn,
> struct hash_alg_common *alg,
> struct crypto_instance *inst);
>
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