From: Eric Biggers <ebigg...@google.com>
Keys for "authenc" AEADs are formatted as an rtattr containing a 4-byte
'enckeylen', followed by an authentication key and an encryption key.
crypto_authenc_extractkeys() parses the key to find the inner keys.
However, it fails to consider the case where the rtattr's payload is
longer than 4 bytes but not 4-byte aligned, and where the key ends
before the next 4-byte aligned boundary. In this case, 'keylen -=
RTA_ALIGN(rta->rta_len);' underflows to a value near UINT_MAX. This
causes a buffer overread and crash during crypto_ahash_setkey().
Fix it by restricting the rtattr payload to the expected size.
Reproducer using AF_ALG:
#include <linux/if_alg.h>
#include <linux/rtnetlink.h>
#include <sys/socket.h>
int main()
{
int fd;
struct sockaddr_alg addr = {
.salg_type = "aead",
.salg_name = "authenc(hmac(sha256),cbc(aes))",
};
struct {
struct rtattr attr;
__be32 enckeylen;
char keys[1];
} __attribute__((packed)) key = {
.attr.rta_len = sizeof(key),
.attr.rta_type = 1 /* CRYPTO_AUTHENC_KEYA_PARAM */,
};
fd = socket(AF_ALG, SOCK_SEQPACKET, 0);
bind(fd, (void *)&addr, sizeof(addr));
setsockopt(fd, SOL_ALG, ALG_SET_KEY, &key, sizeof(key));
}
It caused:
BUG: unable to handle kernel paging request at ffff88007ffdc000
PGD 2e01067 P4D 2e01067 PUD 2e04067 PMD 2e05067 PTE 0
Oops: 0000 [#1] SMP
CPU: 0 PID: 883 Comm: authenc Not tainted
4.20.0-rc1-00108-g00c9fe37a7f27 #13
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.12.0-20181126_142135-anatol 04/01/2014
RIP: 0010:sha256_ni_transform+0xb3/0x330
arch/x86/crypto/sha256_ni_asm.S:155
[...]
Call Trace:
sha256_ni_finup+0x10/0x20 arch/x86/crypto/sha256_ssse3_glue.c:321
crypto_shash_finup+0x1a/0x30 crypto/shash.c:178
shash_digest_unaligned+0x45/0x60 crypto/shash.c:186
crypto_shash_digest+0x24/0x40 crypto/shash.c:202
hmac_setkey+0x135/0x1e0 crypto/hmac.c:66
crypto_shash_setkey+0x2b/0xb0 crypto/shash.c:66
shash_async_setkey+0x10/0x20 crypto/shash.c:223
crypto_ahash_setkey+0x2d/0xa0 crypto/ahash.c:202
crypto_authenc_setkey+0x68/0x100 crypto/authenc.c:96
crypto_aead_setkey+0x2a/0xc0 crypto/aead.c:62
aead_setkey+0xc/0x10 crypto/algif_aead.c:526
alg_setkey crypto/af_alg.c:223 [inline]
alg_setsockopt+0xfe/0x130 crypto/af_alg.c:256
__sys_setsockopt+0x6d/0xd0 net/socket.c:1902
__do_sys_setsockopt net/socket.c:1913 [inline]
__se_sys_setsockopt net/socket.c:1910 [inline]
__x64_sys_setsockopt+0x1f/0x30 net/socket.c:1910
do_syscall_64+0x4a/0x180 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Fixes: e236d4a89a2f ("[CRYPTO] authenc: Move enckeylen into key itself")
Cc: <sta...@vger.kernel.org> # v2.6.25+
Signed-off-by: Eric Biggers <ebigg...@google.com>
---
crypto/authenc.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/crypto/authenc.c b/crypto/authenc.c
index 37f54d1b2f669..4be293a4b5f0f 100644
--- a/crypto/authenc.c
+++ b/crypto/authenc.c
@@ -58,14 +58,22 @@ int crypto_authenc_extractkeys(struct crypto_authenc_keys
*keys, const u8 *key,
return -EINVAL;
if (rta->rta_type != CRYPTO_AUTHENC_KEYA_PARAM)
return -EINVAL;
- if (RTA_PAYLOAD(rta) < sizeof(*param))
+
+ /*
+ * RTA_OK() didn't align the rtattr's payload when validating that it
+ * fits in the buffer. Yet, the keys should start on the next 4-byte
+ * aligned boundary. To avoid confusion, require that the rtattr
+ * payload be exactly the param struct, which has a 4-byte aligned size.
+ */
+ if (RTA_PAYLOAD(rta) != sizeof(*param))
return -EINVAL;
+ BUILD_BUG_ON(sizeof(*param) % RTA_ALIGNTO);
param = RTA_DATA(rta);
keys->enckeylen = be32_to_cpu(param->enckeylen);
- key += RTA_ALIGN(rta->rta_len);
- keylen -= RTA_ALIGN(rta->rta_len);
+ key += rta->rta_len;
+ keylen -= rta->rta_len;
if (keylen < keys->enckeylen)
return -EINVAL;
--
2.19.2
