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Subject[PATCH 4.9 05/39] X.509: fix BUG_ON() when hash algorithm is unsupported
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

commit 437499eea4291ae9621e8763a41df027c110a1ef upstream.

The X.509 parser mishandles the case where the certificate's signature's
hash algorithm is not available in the crypto API. In this case,
x509_get_sig_params() doesn't allocate the cert->sig->digest buffer;
this part seems to be intentional. However,
public_key_verify_signature() is still called via
x509_check_for_self_signed(), which triggers the 'BUG_ON(!sig->digest)'.

Fix this by making public_key_verify_signature() return -ENOPKG if the
hash buffer has not been allocated.

Reproducer when all the CONFIG_CRYPTO_SHA512* options are disabled:

openssl req -new -sha512 -x509 -batch -nodes -outform der \
| keyctl padd asymmetric desc @s

Fixes: 6c2dc5ae4ab7 ("X.509: Extract signature digest and make self-signed cert checks earlier")
Reported-by: Paolo Valente <paolo.valente@linaro.org>
Cc: Paolo Valente <paolo.valente@linaro.org>
Cc: <stable@vger.kernel.org> # v4.7+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
crypto/asymmetric_keys/public_key.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -93,9 +93,11 @@ int public_key_verify_signature(const st

BUG_ON(!pkey);
BUG_ON(!sig);
- BUG_ON(!sig->digest);
BUG_ON(!sig->s);

+ if (!sig->digest)
+ return -ENOPKG;
+
alg_name = sig->pkey_algo;
if (strcmp(sig->pkey_algo, "rsa") == 0) {
/* The data wangled by the RSA algorithm is typically padded

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