linux-kernel - Re: [PATCH] X.509: Fix certificate gathering again

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Date:	Fri, 20 Feb 2015 23:10:12 +0100
From:	Michal Marek <mmarek@...e.cz>
To:	David Howells <dhowells@...hat.com>
Cc:	keyrings@...ux-nfs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] X.509: Fix certificate gathering again

On Fri, Feb 20, 2015 at 02:52:14PM +0100, Michal Marek wrote:
> On 2015-02-19 13:26, David Howells wrote:
> > Michal Marek <mmarek@...e.cz> wrote:
> > 
> >> +X509_CERTIFICATES-y := $(wildcard *.x509)
> >> +ifneq ($(objtree),$(srctree))
> >> +X509_CERTIFICATES-y += $(wildcard $(srctree)/*.x509)
> >> +endif
> >> +X509_CERTIFICATES-$(CONFIG_MODULE_SIG) += signing_key.x509
> >> +X509_CERTIFICATES := $(sort $(X509_CERTIFICATES-y))
> > 
> > What will happen if there's a "signing_key.x509" in the source tree when O= is
> > used?
> 
> It will fail. So the patch needs more work, thanks for the review.

OK, this works for me and I finally understand why :). The problem is
that whatever file make sees (as a target or dependency) first, it will
prefer it for the purpose of VPATH search, so the right signing_key.x509
must come first.  Unfortunately, using 'vpath %.x509' does not do the
trick, because this merely says not to use any special VPATH for files
matching this pattern, but it does not avoid the global VPATH.

>From 1774298ef0fa770cd7e8810ed57ceb4e8a7c5def Mon Sep 17 00:00:00 2001
From: Michal Marek <mmarek@...e.cz>
Date: Wed, 8 Oct 2014 13:15:28 +0200
Subject: [PATCH] X.509: Fix certificate gathering again

Commit d7ec435f (X.509: Fix certificate gathering) fixed the issue of
changing .x509.list, but in the CONFIG_MODULE_SIG=y case, it assumed
that $(objtree) was an absolute path. Commit 7e1c0477 (kbuild: Use
relative path for $(objtree)) broke this assumption and we get
uncecessary rebuilds again, due to ./signing_key.x509 changing to
signing_key.x509. Instead of prepending the absolute path and
stripping it again, just check if $(srctree) and $(objtree) are
different directories and add $(srctree)/*.x509 only in such case.

However, such fix causes a different issue, namely that a potential
$(srctree)/signing_key.x509 appears before the to-be-generated
signing_key.x509 in the sorted list, and make remembers this file for
the purpose of VPATH search. It worked previously, because
./signing_key.x509 sorts before any absolute path. Solve this by sorting
the $(objtree) and $(srctree) files separately, to ensure that
signing_key.x509 appears before anything from $(srctree).

Signed-off-by: Michal Marek <mmarek@...e.cz>
---
 kernel/Makefile | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/kernel/Makefile b/kernel/Makefile
index 1408b33..792e043 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -117,17 +117,18 @@ $(obj)/config_data.h: $(obj)/config_data.gz FORCE
 # boot.
 #
 # We look in the source root and the build root for all files whose name ends
-# in ".x509".  Unfortunately, this will generate duplicate filenames, so we
-# have make canonicalise the pathnames and then sort them to discard the
-# duplicates.
+# in ".x509". We put the $(objtree) certificates before those from $(srctree),
+# so that a potential signing_key.x509 file from $(srctree) does not take
+# precedence.
 #
 ###############################################################################
 ifeq ($(CONFIG_SYSTEM_TRUSTED_KEYRING),y)
-X509_CERTIFICATES-y := $(wildcard *.x509) $(wildcard $(srctree)/*.x509)
-X509_CERTIFICATES-$(CONFIG_MODULE_SIG) += $(objtree)/signing_key.x509
-X509_CERTIFICATES-raw := $(sort $(foreach CERT,$(X509_CERTIFICATES-y), \
-				$(or $(realpath $(CERT)),$(CERT))))
-X509_CERTIFICATES := $(subst $(realpath $(objtree))/,,$(X509_CERTIFICATES-raw))
+X509_CERTIFICATES-y := $(wildcard *.x509)
+X509_CERTIFICATES-$(CONFIG_MODULE_SIG) += signing_key.x509
+X509_CERTIFICATES := $(sort $(X509_CERTIFICATES-y))
+ifneq ($(objtree),$(srctree))
+X509_CERTIFICATES += $(sort $(wildcard $(srctree)/*.x509))
+endif

 ifeq ($(X509_CERTIFICATES),)
 $(warning *** No X.509 certificates found ***)
-- 
1.9.2

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