Re: [PATCH] fs: select: fix information leak to userspace

[Andreas Dilger]

On 2010-11-12, at 13:08, Andrew Morton wrote:
> On Wed, 10 Nov 2010 23:38:02 +0300
> Vasiliy Kulikov <segooon@xxxxxxxxx> wrote:
>> On some architectures __kernel_suseconds_t is int.
> 
> On sparc and parisc.  On all other architectures this patch is a waste
> of cycles.
> 
> --- a/fs/select.c~fs-select-fix-information-leak-to-userspace-fix
> +++ a/fs/select.c
> @@ -306,7 +306,8 @@ static int poll_select_copy_remaining(st
> 		rts.tv_sec = rts.tv_nsec = 0;
> 
> 	if (timeval) {
> -		memset(&rtv, 0, sizeof(rtv));
> +		if (sizeof(rtv) > sizeof(rtv.tv_sec) + sizeof(rtv.tv_usec))
> +			memset(&rtv, 0, sizeof(rtv));
> 		rtv.tv_sec = rts.tv_sec;
> 		rtv.tv_usec = rts.tv_nsec / NSEC_PER_USEC;
> 
> _
> 
> 
> The `if' gets eliminated at compile time.  With this approach we add
> four bytes of text to the sparc64 build and zero bytes of text to the
> x86_64 build.

It's nice to have comments (or at least a good commit message) for unusual code like this, so that in the future it is clear when this kind of workaround can be removed (e.g. if the time_t is changed to always be a 64-bit value for Y2038 issues, even on 32-bit arches). 

Cheers, Andreas





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