linux-kernel - Re: [PATCH] lib: test_user

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Date:   Sun, 6 Oct 2019 10:41:03 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Aleksa Sarai <cyphar@...har.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib: test_user_copy: style cleanup

On Sun, Oct 06, 2019 at 10:30:28AM +1100, Aleksa Sarai wrote:
> While writing the tests for copy_struct_from_user(), I used a construct
> that Linus doesn't appear to be too fond of:
> 
> On 2019-10-04, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > Hmm. That code is ugly, both before and after the fix.
> >
> > This just doesn't make sense for so many reasons:
> >
> >         if ((ret |= test(umem_src == NULL, "kmalloc failed")))
> >
> > where the insanity comes from
> >
> >  - why "|=" when you know that "ret" was zero before (and it had to
> >    be, for the test to make sense)
> >
> >  - why do this as a single line anyway?
> >
> >  - don't do the stupid "double parenthesis" to hide a warning. Make it
> >    use an actual comparison if you add a layer of parentheses.
> 
> So instead, use a bog-standard check that isn't nearly as ugly.
> 
> Fixes: 341115822f88 ("usercopy: Add parentheses around assignment in test_copy_struct_from_user")
> Fixes: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
> Signed-off-by: Aleksa Sarai <cyphar@...har.com>

Fwiw, I think the commit message doesn't necessarily need to mention
stylistic preferences nor a specific mail. It's sufficient enough to say
that the new way makes things way more obvious. But ok. :)

I'll pick this up now.

Reviewed-by: Christian Brauner <christian.brauner@...ntu.com>