netdev - Re: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu,  3 Mar 2022 16:30:07 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     jakobkoschel@...il.com
Cc:     David.Laight@...LAB.COM, akpm@...ux-foundation.org,
        alsa-devel@...a-project.org, amd-gfx@...ts.freedesktop.org,
        andriy.shevchenko@...ux.intel.com, arnd@...db.de,
        bcm-kernel-feedback-list@...adcom.com, bjohannesmeyer@...il.com,
        c.giuffrida@...nl, christian.koenig@....com,
        christophe.jaillet@...adoo.fr, dan.carpenter@...cle.com,
        dmaengine@...r.kernel.org, drbd-dev@...ts.linbit.com,
        dri-devel@...ts.freedesktop.org, gustavo@...eddedor.com,
        h.j.bos@...nl, intel-gfx@...ts.freedesktop.org,
        intel-wired-lan@...ts.osuosl.org, jgg@...pe.ca,
        keescook@...omium.org, kgdb-bugreport@...ts.sourceforge.net,
        kvm@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-block@...r.kernel.org,
        linux-cifs@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-pm@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-sgx@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-tegra@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-wireless@...r.kernel.org,
        linux1394-devel@...ts.sourceforge.net, linux@...musvillemoes.dk,
        linuxppc-dev@...ts.ozlabs.org, nathan@...nel.org,
        netdev@...r.kernel.org, nouveau@...ts.freedesktop.org,
        rppt@...nel.org, samba-technical@...ts.samba.org,
        tglx@...utronix.de, tipc-discussion@...ts.sourceforge.net,
        torvalds@...ux-foundation.org,
        v9fs-developer@...ts.sourceforge.net, xiam0nd.tong@...il.com
Subject: Re: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr

> I think this would make sense, it would mean you only assign the containing
> element on valid elements.
>
> I was thinking something along the lines of:
>
> #define list_for_each_entry(pos, head, member)					\
>	for (struct list_head *list = head->next, typeof(pos) pos;	\
>	     list == head ? 0 : (( pos = list_entry(pos, list, member), 1));	\
>	     list = list->next)
>
> Although the initialization block of the for loop is not valid C, I'm
> not sure there is any way to declare two variables of a different type
> in the initialization part of the loop.

It can be done using a *nested loop*, like this:

#define list_for_each_entry(pos, head, member)					\
	for (struct list_head *list = head->next, cond = (struct list_head *)-1; cond == (struct list_head *)-1; cond = NULL) \
	  for (typeof(pos) pos;	\
	     list == head ? 0 : (( pos = list_entry(pos, list, member), 1));	\
	     list = list->next)

>
> I believe all this does is get rid of the &pos->member == (head) check
> to terminate the list.

Indeed, although the original way is harmless.

> It alone will not fix any of the other issues that using the iterator
> variable after the loop currently has.

Yes, but I stick with the list_for_each_entry_inside(pos, type, head, member)
way to make the iterator invisiable outside the loop (before and after the loop).
It is maintainable longer-term than "type(pos) pos" one and perfect.
see my explain:
https://lore.kernel.org/lkml/20220302093106.8402-1-xiam0nd.tong@gmail.com/
and list_for_each_entry_inside(pos, type, head, member) patch here:
https://lore.kernel.org/lkml/20220301075839.4156-3-xiam0nd.tong@gmail.com/

--
Xiaomeng Tong