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authorEric Biggers <ebiggers@google.com>2018-02-22 14:38:33 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-02-28 10:19:39 +0100
commit1a1f7f726bd8670b7b371f4e440533cdcb9d8110 (patch)
treec3c4ccf1f10c378ad89ed2c0aea1f8bc21a4dd82
parent99b2095ac71e316ed366f027913646d40640d0be (diff)
PKCS#7: fix certificate chain verification
commit 971b42c038dc83e3327872d294fe7131bab152fc upstream. When pkcs7_verify_sig_chain() is building the certificate chain for a SignerInfo using the certificates in the PKCS#7 message, it is passing the wrong arguments to public_key_verify_signature(). Consequently, when the next certificate is supposed to be used to verify the previous certificate, the next certificate is actually used to verify itself. An attacker can use this bug to create a bogus certificate chain that has no cryptographic relationship between the beginning and end. Fortunately I couldn't quite find a way to use this to bypass the overall signature verification, though it comes very close. Here's the reasoning: due to the bug, every certificate in the chain beyond the first actually has to be self-signed (where "self-signed" here refers to the actual key and signature; an attacker might still manipulate the certificate fields such that the self_signed flag doesn't actually get set, and thus the chain doesn't end immediately). But to pass trust validation (pkcs7_validate_trust()), either the SignerInfo or one of the certificates has to actually be signed by a trusted key. Since only self-signed certificates can be added to the chain, the only way for an attacker to introduce a trusted signature is to include a self-signed trusted certificate. But, when pkcs7_validate_trust_one() reaches that certificate, instead of trying to verify the signature on that certificate, it will actually look up the corresponding trusted key, which will succeed, and then try to verify the *previous* certificate, which will fail. Thus, disaster is narrowly averted (as far as I could tell). Fixes: 6c2dc5ae4ab7 ("X.509: Extract signature digest and make self-signed cert checks earlier") 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>
-rw-r--r--crypto/asymmetric_keys/pkcs7_verify.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
index 986033e64a83..d418b725dfef 100644
--- a/crypto/asymmetric_keys/pkcs7_verify.c
+++ b/crypto/asymmetric_keys/pkcs7_verify.c
@@ -273,7 +273,7 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
sinfo->index);
return 0;
}
- ret = public_key_verify_signature(p->pub, p->sig);
+ ret = public_key_verify_signature(p->pub, x509->sig);
if (ret < 0)
return ret;
x509->signer = p;