PKCS#7: Introduce pkcs7_get_digest()

IMA will need to access the digest of the PKCS7 message (as calculated by
the kernel) before the signature is verified, so introduce
pkcs7_get_digest() for that purpose.

Also, modify pkcs7_digest() to detect when the digest was already
calculated so that it doesn't have to do redundant work. Verifying that
sinfo->sig->digest isn't NULL is sufficient because both places which
allocate sinfo->sig (pkcs7_parse_message() and pkcs7_note_signed_info())
use kzalloc() so sig->digest is always initialized to zero.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
index 96071bee03ac..38ec7f5f9041 100644
--- a/include/crypto/pkcs7.h
+++ b/include/crypto/pkcs7.h
@@ -9,6 +9,7 @@
 #define _CRYPTO_PKCS7_H
 
 #include <linux/verification.h>
+#include <linux/hash_info.h>
 #include <crypto/public_key.h>
 
 struct key;
@@ -40,4 +41,7 @@ extern int pkcs7_verify(struct pkcs7_message *pkcs7,
 extern int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
                                       const void *data, size_t datalen);
 
+extern int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf,
+                            u32 *len, enum hash_algo *hash_algo);
+
 #endif /* _CRYPTO_PKCS7_H */