From: Eric Biggers <>

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 <>
Cc: Paolo Valente <>
Cc: <> # v4.7+
Signed-off-by: Eric Biggers <>
Signed-off-by: David Howells <>

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

diff --git a/crypto/asymmetric_keys/public_key.c 
index de996586762a..e929fe1e4106 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -79,9 +79,11 @@ int public_key_verify_signature(const struct public_key 
-       BUG_ON(!sig->digest);
+       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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