On Tue, May 14, 2019 at 04:13:15PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> The "hmac(sha3-224-generic)" algorithm has a descsize of 368 bytes,
> which is greater than HASH_MAX_DESCSIZE (360) which is only enough for
> sha3-224-generic. The check in shash_prepare_alg() doesn't catch this
> because the HMAC template doesn't set descsize on the algorithms, but
> rather sets it on each individual HMAC transform.
>
> This causes a stack buffer overflow when SHASH_DESC_ON_STACK() is used
> with hmac(sha3-224-generic).
>
> Fix it by increasing HASH_MAX_DESCSIZE to the real maximum. Also add a
> sanity check to hmac_init().
>
> This was detected by the improved crypto self-tests in v5.2, by loading
> the tcrypt module with CONFIG_CRYPTO_MANAGER_EXTRA_TESTS=y enabled. I
> didn't notice this bug when I ran the self-tests by requesting the
> algorithms via AF_ALG (i.e., not using tcrypt), probably because the
> stack layout differs in the two cases and that made a difference here.
>
> KASAN report:
>
> BUG: KASAN: stack-out-of-bounds in memcpy include/linux/string.h:359 [inline]
> BUG: KASAN: stack-out-of-bounds in shash_default_import+0x52/0x80 crypto/shash.c:223
> Write of size 360 at addr ffff8880651defc8 by task insmod/3689
>
> CPU: 2 PID: 3689 Comm: insmod Tainted: G E 5.1.0-10741-g35c99ffa20edd #11
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x86/0xc5 lib/dump_stack.c:113
> print_address_description+0x7f/0x260 mm/kasan/report.c:188
> __kasan_report+0x144/0x187 mm/kasan/report.c:317
> kasan_report+0x12/0x20 mm/kasan/common.c:614
> check_memory_region_inline mm/kasan/generic.c:185 [inline]
> check_memory_region+0x137/0x190 mm/kasan/generic.c:191
> memcpy+0x37/0x50 mm/kasan/common.c:125
> memcpy include/linux/string.h:359 [inline]
> shash_default_import+0x52/0x80 crypto/shash.c:223
> crypto_shash_import include/crypto/hash.h:880 [inline]
> hmac_import+0x184/0x240 crypto/hmac.c:102
> hmac_init+0x96/0xc0 crypto/hmac.c:107
> crypto_shash_init include/crypto/hash.h:902 [inline]
> shash_digest_unaligned+0x9f/0xf0 crypto/shash.c:194
> crypto_shash_digest+0xe9/0x1b0 crypto/shash.c:211
> generate_random_hash_testvec.constprop.11+0x1ec/0x5b0 crypto/testmgr.c:1331
> test_hash_vs_generic_impl+0x3f7/0x5c0 crypto/testmgr.c:1420
> __alg_test_hash+0x26d/0x340 crypto/testmgr.c:1502
> alg_test_hash+0x22e/0x330 crypto/testmgr.c:1552
> alg_test.part.7+0x132/0x610 crypto/testmgr.c:4931
> alg_test+0x1f/0x40 crypto/testmgr.c:4952
>
> Fixes: b68a7ec1e9a3 ("crypto: hash - Remove VLA usage")
> Reported-by: Corentin Labbe <clabbe.montjoie@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.20+
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Ah, yikes! Nice catch. Thanks for fixing this. :)
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
--
Kees Cook
