Re: [PATCH] dcache: error out on failures to store terminating NUL

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Jan 24, 2014 at 01:17:46PM +0100, Denys Vlasenko wrote:
> A number of routines wasn't checking that the initial call
> to prepend "\0" to result buffer doesn't fail.
> 
> Coredump code was seeing d_path() with zero-sized buffer
> to erroneously return bogus data (non-error pointer
> pointing before buffer start).
> 
> Users report that this change fixes it.

NAK.  Again, this is not dealing with overflows - it's basic sanity
check on arguments.  Choose which level should that be done at and
just do it there.  As in "if (!buflen) return -ENAMETOOLONG;".
>  		char *cwd = page + PATH_MAX;
>  		int buflen = PATH_MAX;
>  
> -		prepend(&cwd, &buflen, "\0", 1);
> -		error = prepend_path(&pwd, &root, &cwd, &buflen);
> +		error = prepend(&cwd, &buflen, "\0", 1);
> +		if (!error)
> +			error = prepend_path(&pwd, &root, &cwd, &buflen);

Ah, yes - the dreadful case of zero PATH_MAX...