[Skiboot] [PATCH 3/3] secvar/pkcs7: fix a wrong sizeof()

[Daniel Axtens]

This code isn't directly used by skiboot, but it is wrong and potentially
insecure so I'm fixing it in case it's used in the future.

We pass sizeof(hash) into mbedtls_pk_verify(). However, hash is a pointer,
not an array, so rather than passing the length of the hash to verify we'll
pass in 8, and only compare the first 8 bytes of the hash rather than all 32.

Pass in 0 instead. That tells mbedtls to work out the length based on the
hash type. We allocated enough memory for whatever hash type the PKCS#7
message declared so this will be safe.

Signed-off-by: Daniel Axtens <dja at axtens.net>
---
 libstb/crypto/pkcs7/pkcs7.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstb/crypto/pkcs7/pkcs7.c b/libstb/crypto/pkcs7/pkcs7.c
index 4407e201a4cc..3f41ba7acb2e 100644
--- a/libstb/crypto/pkcs7/pkcs7.c
+++ b/libstb/crypto/pkcs7/pkcs7.c
@@ -538,7 +538,7 @@ int mbedtls_pkcs7_signed_data_verify( mbedtls_pkcs7 *pkcs7,
 
     mbedtls_md( md_info, data, datalen, hash );
 
-    ret = mbedtls_pk_verify( &pk_cxt, md_alg, hash, sizeof(hash),
+    ret = mbedtls_pk_verify( &pk_cxt, md_alg, hash, 0,
                                       pkcs7->signed_data.signers.sig.p,
                                       pkcs7->signed_data.signers.sig.len );
 
-- 
2.27.0