2021-10-18 03:37:13

by Matthew Wilcox

Subject: Re: [PATCH] sysctl: Avoid open coded arithmetic in memory allocator functions

On Sat, Oct 16, 2021 at 05:28:28PM +0200, Len Baker wrote:
> +static size_t new_dir_size(size_t namelen)
> +{
> + size_t bytes;
> +
> + if (check_add_overflow(sizeof(struct ctl_dir), sizeof(struct ctl_node),
> + &bytes))
> + return SIZE_MAX;
> + if (check_add_overflow(bytes, array_size(sizeof(struct ctl_table), 2),
> + &bytes))
> + return SIZE_MAX;
> + if (check_add_overflow(bytes, namelen, &bytes))
> + return SIZE_MAX;
> + if (check_add_overflow(bytes, (size_t)1, &bytes))
> + return SIZE_MAX;
> +
> + return bytes;
> +}

I think this is overkill. All these structs are small and namelen is
supplied by the kernel, not specified by userspace. It really complicates
the code, and I don't see the advantage.

2021-10-23 10:40:18

by Len Baker

Subject: Re: [PATCH] sysctl: Avoid open coded arithmetic in memory allocator functions

Hi Matthew,

On Sat, Oct 16, 2021 at 05:18:24PM +0100, Matthew Wilcox wrote:
> On Sat, Oct 16, 2021 at 05:28:28PM +0200, Len Baker wrote:
> > +static size_t new_dir_size(size_t namelen)
> > +{
> > + size_t bytes;
> > +
> > + if (check_add_overflow(sizeof(struct ctl_dir), sizeof(struct ctl_node),
> > + &bytes))
> > + return SIZE_MAX;
> > + if (check_add_overflow(bytes, array_size(sizeof(struct ctl_table), 2),
> > + &bytes))
> > + return SIZE_MAX;
> > + if (check_add_overflow(bytes, namelen, &bytes))
> > + return SIZE_MAX;
> > + if (check_add_overflow(bytes, (size_t)1, &bytes))
> > + return SIZE_MAX;
> > +
> > + return bytes;
> > +}
>
> I think this is overkill. All these structs are small and namelen is
> supplied by the kernel, not specified by userspace. It really complicates
> the code, and I don't see the advantage.
>
Ok, understood. I will send a v2 without this function.

Thanks for the review,
Len