linux-kernel - Re: [PATCH] x86/uv/time: Replace one-element array and save heap space

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Date:   Mon, 18 May 2020 17:32:02 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org H. Peter Anvin" <hpa@...or.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] x86/uv/time: Replace one-element array and save heap
 space

On Mon, May 18, 2020 at 12:09:16PM -0700, Joe Perches wrote:
> On Mon, 2020-05-18 at 14:01 -0500, Gustavo A. R. Silva wrote:
> > The current codebase makes use of one-element arrays in the following
> > form:
> > 
> > struct something {
> >     int length;
> >     u8 data[1];
> > };
> []
> > This issue has been out there since 2009.
> > This issue was found with the help of Coccinelle and fixed _manually_.
> []
> > diff --git a/arch/x86/platform/uv/uv_time.c b/arch/x86/platform/uv/uv_time.c
> > index 7af31b245636..993a8ae6fdfb 100644
> > --- a/arch/x86/platform/uv/uv_time.c
> > +++ b/arch/x86/platform/uv/uv_time.c
> > @@ -52,7 +52,7 @@ struct uv_rtc_timer_head {
> >  	struct {
> >  		int	lcpu;		/* systemwide logical cpu number */
> >  		u64	expires;	/* next timer expiration for this cpu */
> > -	} cpu[1];
> > +	} cpu[];
> >  };
> >  
> >  /*
> > @@ -156,9 +156,8 @@ static __init int uv_rtc_allocate_timers(void)
> >  		struct uv_rtc_timer_head *head = blade_info[bid];
> >  
> >  		if (!head) {
> > -			head = kmalloc_node(sizeof(struct uv_rtc_timer_head) +
> > -				(uv_blade_nr_possible_cpus(bid) *
> > -					2 * sizeof(u64)),
> > +			head = kmalloc_node(struct_size(head, cpu,
> > +				uv_blade_nr_possible_cpus(bid)),
> 
> It's probably safer to use kzalloc_node here as well.
> 

Thanks for your feedback, Joe. I'll wait for comments from the
maintainers on this and the rest of the patch.

Thanks
--
Gustavo

> >  				GFP_KERNEL, nid);
> >  			if (!head) {
> >  				uv_rtc_deallocate_timers();
>