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>
af3ff8045b