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List:       linux-kernel
Subject:    Re: [PATCH] x86/audit: fix -Wmissing-variable-declarations warning for ia32_xyz_class
From:       Justin Stitt <justinstitt () google ! com>
Date:       2023-08-31 23:18:10
Message-ID: CAFhGd8rZdRw1EX-=d7o57TqUc2OacNK-Uciniup=bvtyfsoxgw () mail ! gmail ! com
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On Thu, Aug 31, 2023 at 2:11 PM Kees Cook <keescook@chromium.org> wrote:
> 
> On Tue, Aug 29, 2023 at 10:33:16PM +0000, Justin Stitt wrote:
> > When building x86 defconfig with Clang-18 I get the following warnings:
> > > arch/x86/ia32/audit.c:6:10: warning: no previous extern declaration for non-static variable \
> > > 'ia32_dir_class' [-Wmissing-variable-declarations]
> > > 6 | unsigned ia32_dir_class[] = {
> > > arch/x86/ia32/audit.c:11:10: warning: no previous extern declaration for non-static variable \
> > > 'ia32_chattr_class' [-Wmissing-variable-declarations]
> > > 11 | unsigned ia32_chattr_class[] = {
> > > arch/x86/ia32/audit.c:16:10: warning: no previous extern declaration for non-static variable \
> > > 'ia32_write_class' [-Wmissing-variable-declarations]
> > > 16 | unsigned ia32_write_class[] = {
> > > arch/x86/ia32/audit.c:21:10: warning: no previous extern declaration for non-static variable \
> > > 'ia32_read_class' [-Wmissing-variable-declarations]
> > > 21 | unsigned ia32_read_class[] = {
> > > arch/x86/ia32/audit.c:26:10: warning: no previous extern declaration for non-static variable \
> > > 'ia32_signal_class' [-Wmissing-variable-declarations]
> > > 26 | unsigned ia32_signal_class[] = {
> > 
> > These warnings occur due to their respective extern declarations being
> > scoped inside of audit_classes_init as well as only being enabled with
> > `CONFIG_IA32_EMULATION=y`:
> > > static int __init audit_classes_init(void)
> > > {
> > > #ifdef CONFIG_IA32_EMULATION
> > > extern __u32 ia32_dir_class[];
> > > extern __u32 ia32_write_class[];
> > > extern __u32 ia32_read_class[];
> > > extern __u32 ia32_chattr_class[];
> > > audit_register_class(AUDIT_CLASS_WRITE_32, ia32_write_class);
> > > audit_register_class(AUDIT_CLASS_READ_32, ia32_read_class);
> > > audit_register_class(AUDIT_CLASS_DIR_WRITE_32, ia32_dir_class);
> > > audit_register_class(AUDIT_CLASS_CHATTR_32, ia32_chattr_class);
> > > #endif
> > > audit_register_class(AUDIT_CLASS_WRITE, write_class);
> > > audit_register_class(AUDIT_CLASS_READ, read_class);
> > > audit_register_class(AUDIT_CLASS_DIR_WRITE, dir_class);
> > > audit_register_class(AUDIT_CLASS_CHATTR, chattr_class);
> > > return 0;
> > > }
> > 
> > Lift the extern declarations to their own header and resolve scoping
> > issues (and thus fix the warnings).
> > 
> > Moreover, change __u32 to unsigned so that we match the definitions:
> > > unsigned ia32_dir_class[] = {
> > > #include <asm-generic/audit_dir_write.h>
> > > ~0U
> > > };
> > > 
> > > unsigned ia32_chattr_class[] = {
> > > #include <asm-generic/audit_change_attr.h>
> > > ~0U
> > > };
> > > ...
> 
> I would expect checkpatch to warn about bare "unsigned", which is frown
> on these days. :) I think __u32 should be fine here...? (Why is it __u32
> instead of u32, btw?)

Yeah, checkpatch doesn't like it. I was just trying to mirror the
implementation in audit.c as closely as possible:
> unsigned ia32_dir_class[] = {
> #include <asm-generic/audit_dir_write.h>
> ~0U
> };


> 
> But otherwise, yes, looks good.

Thanks for the feedback here. Should I send a v2 where I changed _all_
instances of `unsigned` in both audit.c and audit.h to be `u32`? Or
perhaps, `unsigned int`.

> 
> -Kees
> 
> --
> Kees Cook


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