Re: libbacktrace patch RFC: check size passed to backtrace_get_view

[Tom de Vries <tdevries@suse.de>]

On 18-01-19 16:40, Ian Lance Taylor wrote:
>  int
>  backtrace_get_view (struct backtrace_state *state ATTRIBUTE_UNUSED,
> -		    int descriptor, off_t offset, size_t size,
> +		    int descriptor, off_t offset, uint64_t size,
>  		    backtrace_error_callback error_callback,
>  		    void *data, struct backtrace_view *view)
>  {
> @@ -60,6 +60,12 @@ backtrace_get_view (struct backtrace_sta
>    off_t pageoff;
>    void *map;
>  
> +  if ((uint64_t) (size_t) size != size)
> +    {
> +      error_callback (data, "file size too large", 0);
> +      return 0;
> +    }
> +

Agreed, this will fix the PR.

There's a cornercase I'm not sure is worth bothering about, but given
that this is an RFC: in the case of 32-bit systems with 32-bit
filesystem, there will be a range of numbers that fit in size_t, but are
too large for off_t (both 32-bit but size_t unsigned and off_t signed),
so in that case, the file size is too large, but we're not detecting
that here. Though I think that should be handled in the subsequent mmap
(or, in the case of read.c, in the subsequent read(), though I'm
guessing the earlier backtrace_alloc > 2GB will already fail).

Thanks,
- Tom