linux-kernel - Re: [PATCH v3] seccomp: Add find

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Message-ID: <202006171420.C8007EDCD8@keescook>
Date:   Wed, 17 Jun 2020 14:22:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Sargun Dhillon <sargun@...gun.me>,
        containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
        christian.brauner@...ntu.com, cyphar@...har.com, jannh@...gle.com,
        jeffv@...gle.com, palmer@...gle.com, rsesek@...gle.com,
        tycho@...ho.ws, Matt Denton <mpdenton@...gle.com>
Subject: Re: [PATCH v3] seccomp: Add find_notification helper

On Wed, Jun 17, 2020 at 01:08:44PM -0700, Nathan Chancellor wrote:
> On Mon, Jun 01, 2020 at 04:25:32AM -0700, Sargun Dhillon wrote:
> > [...]
> >  static long seccomp_notify_recv(struct seccomp_filter *filter,
> >  				void __user *buf)
> >  {
> > -	struct seccomp_knotif *knotif = NULL, *cur;
> > +	struct seccomp_knotif *knotif, *cur;
> >  	struct seccomp_notif unotif;
> >  	ssize_t ret;
> >  
> 
> I don't know that this should have been removed, clang now warns:
> 
> kernel/seccomp.c:1063:2: warning: variable 'knotif' is used uninitialized whenever 'for' loop exits because its condition is false [-Wsometimes-uninitialized]
>         list_for_each_entry(cur, &filter->notif->notifications, list) {
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> include/linux/list.h:602:7: note: expanded from macro 'list_for_each_entry'
>              &pos->member != (head);                                    \
>              ^~~~~~~~~~~~~~~~~~~~~~
> kernel/seccomp.c:1075:7: note: uninitialized use occurs here
>         if (!knotif) {
>              ^~~~~~
> kernel/seccomp.c:1063:2: note: remove the condition if it is always true
>         list_for_each_entry(cur, &filter->notif->notifications, list) {
>         ^
> include/linux/list.h:602:7: note: expanded from macro 'list_for_each_entry'
>              &pos->member != (head);                                    \
>              ^
> kernel/seccomp.c:1045:31: note: initialize the variable 'knotif' to silence this warning
>         struct seccomp_knotif *knotif, *cur;
>                                      ^
>                                       = NULL
> 1 warning generated.

Eek; yes, thank you! I've folded the fix into Sargun's patch.

-- 
Kees Cook