linux-kernel - Re: [RFC PATCH v2 01/14] lsm: Only build lsm_audit.c if CONFIG

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Message-ID: <7751320f-cad0-477a-bed0-923dadfcf1cd@roeck-us.net>
Date: Wed, 23 Oct 2024 11:51:02 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Mickaël Salaün <mic@...ikod.net>
Cc: Eric Paris <eparis@...hat.com>, Paul Moore <paul@...l-moore.com>,
	Günther Noack <gnoack@...gle.com>,
	"Serge E . Hallyn" <serge@...lyn.com>,
	Ben Scarlato <akhna@...gle.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Charles Zaffery <czaffery@...lox.com>,
	James Morris <jmorris@...ei.org>, Jann Horn <jannh@...gle.com>,
	Jeff Xu <jeffxu@...gle.com>,
	Jorge Lucangeli Obes <jorgelo@...gle.com>,
	Kees Cook <kees@...nel.org>,
	Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
	Matt Bobrowski <mattbobrowski@...gle.com>,
	Mikhail Ivanov <ivanov.mikhail1@...wei-partners.com>,
	Praveen K Paladugu <prapal@...ux.microsoft.com>,
	Robert Salvet <robert.salvet@...lox.com>,
	Shervin Oloumi <enlightened@...gle.com>, Song Liu <song@...nel.org>,
	Tahera Fahimi <fahimitahera@...il.com>, audit@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [RFC PATCH v2 01/14] lsm: Only build lsm_audit.c if CONFIG_AUDIT
 is set

On Tue, Oct 22, 2024 at 06:09:56PM +0200, Mickaël Salaün wrote:
> When CONFIG_AUDIT is set, its CONFIG_NET dependency is also set, and the
> dev_get_by_index and init_net symbols (used by dump_common_audit_data)
> are found by the linker.  dump_common_audit_data() should then failed to
> build when CONFIG_NET is not set. However, because the compiler is
> smart, it knows that audit_log_start() always return NULL when
> !CONFIG_AUDIT, and it doesn't build the body of common_lsm_audit().  As
> a side effect, dump_common_audit_data() is not built and the linker
> doesn't error out because of missing symbols.
> 
> Let's only build lsm_audit.o when CONFIG_AUDIT is set.
> 

CONFIG_AUDIT and CONFIG_SECURITY are independent of each other.
With CONFIG_SECURITY=n and CONFIG_AUDIT=y, we now get:

Error log:
arm-linux-gnueabi-ld: security/lsm_audit.o: in function `audit_log_lsm_data':
security/lsm_audit.c:417:(.text+0x5e4): undefined reference to `lockdown_reasons'
arm-linux-gnueabi-ld: security/lsm_audit.c:417:(.text+0x5e8): undefined reference to `lockdown_reasons'
make[3]: *** [scripts/Makefile.vmlinux:78: vmlinux] Error 1
make[2]: *** [Makefile:1178: vmlinux] Error 2
make[1]: *** [Makefile:224: __sub-make] Error 2
make: *** [Makefile:224: __sub-make] Error 2

Guenter