linux-kernel - [PATCH 1/1] x509: only prefix strip raw serial numbers

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Date:	Mon, 14 Sep 2015 09:13:37 +0100
From:	Andy Whitcroft <apw@...onical.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>
Cc:	David Howells <dhowells@...hat.com>, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] x509: only prefix strip raw serial numbers

In the commit below we added support for use of the subKeyId rather than
the raw serial number when forming the in kernel ID:

  commit dd2f6c4481debfa389c1f2b2b1d5bd6449c42611
  Author: David Howells <dhowells@...hat.com>
  Date:   Fri Oct 3 16:17:02 2014 +0100

    X.509: If available, use the raw subjKeyId to form the key description

However as part of this we subject the subjKeyId to the below prefix strip:

    if (srlen > 1 && *q == 0) {
	    srlen--;
	    q++;
    }

This leads us to truncate the id for kernel module signing keys and to
fail to recognise our own modules:

  [    1.572423] Loaded X.509 cert 'Build time autogenerated kernel
    key: 62a7c3d2da278be024da4af8652c071f3fea33'
  [    1.646153] Request for unknown module key 'Build time autogenerated
    kernel key: 0062a7c3d2da278be024da4af8652c071f3fea33' err -11

Only apply the prefix strip to raw serial number.

Signed-off-by: Andy Whitcroft <apw@...onical.com>
---
 crypto/asymmetric_keys/x509_public_key.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

	While we are here the prefix strip seems pretty odd, only removing
	just one 0 byte.  Is this meant to strip them all (as a while),
	or was the intent to strip leading 0s from the hex form?  Do we
	have any background to this change?

	-apw

diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 24f17e6..0e16d5e 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -306,10 +306,10 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 	} else {
 		srlen = cert->raw_serial_size;
 		q = cert->raw_serial;
-	}
-	if (srlen > 1 && *q == 0) {
-		srlen--;
-		q++;
+		if (srlen > 1 && *q == 0) {
+			srlen--;
+			q++;
+		}
 	}
 
 	ret = -ENOMEM;
-- 
2.5.0

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