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>
---
crypto/hmac.c | 2 ++
include/crypto/hash.h | 8 +++++++-
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/crypto/hmac.c b/crypto/hmac.c
index a68c1266121f5..241b1868c1d01 100644
--- a/crypto/hmac.c
+++ b/crypto/hmac.c
@@ -157,6 +157,8 @@ static int hmac_init_tfm(struct crypto_tfm *tfm)
parent->descsize = sizeof(struct shash_desc) +
crypto_shash_descsize(hash);
+ if (WARN_ON(parent->descsize > HASH_MAX_DESCSIZE))
+ return -EINVAL;
ctx->hash = hash;
return 0;
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index d21bea2c43829..d6702b4a457f9 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -150,7 +150,13 @@ struct shash_desc {
};
#define HASH_MAX_DIGESTSIZE 64
-#define HASH_MAX_DESCSIZE 360
+
+/*
+ * Worst case is hmac(sha3-224-generic). Its context is a nested 'shash_desc'
+ * containing a 'struct sha3_state'.
+ */
+#define HASH_MAX_DESCSIZE (sizeof(struct shash_desc) + 360)
+
#define HASH_MAX_STATESIZE 512
#define SHASH_DESC_ON_STACK(shash, ctx) \
--
2.21.0.1020.gf2820cf01a-goog
