On Tue, Nov 28, 2017 at 06:01:38PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
