Re: [Qemu-block] [PATCH v2 0/3] Fix strncpy() warnings for GCC8 new -Wstringop-truncation

[Michael S. Tsirkin]

On Tue, Dec 18, 2018 at 05:55:27PM +0100, Philippe Mathieu-Daudé wrote:
> On 12/18/18 3:54 PM, Michael S. Tsirkin wrote:
> > On Tue, Dec 18, 2018 at 03:45:08PM +0100, Paolo Bonzini wrote:
> >> On 18/12/18 15:31, Michael S. Tsirkin wrote:
> >>> Do you happen to know why does it build fine with
> >>> Gcc 8.2.1?
> >>>
> >>> Reading the GCC manual it seems that
> >>> there is a "nostring" attribute that means
> >>> "might not be 0 terminated".
> >>> I think we should switch to that which fixes the warning
> >>> but also warns if someone tries to misuse these
> >>> as C-strings.
> >>>
> >>> Seems to be a better option, does it not?
> >>>
> >>>
> >>
> >> Using strpadcpy is clever and self-documenting, though.  We have it
> >> already, so why not use it.
> >>
> >> Paolo
> > 
> > The advantage of nonstring is that it will catch attempts to
> > use these fields with functions that expect a 0 terminated string.
> > 
> > strpadcpy will instead just silence the warning.
> 
> migration/global_state.c:109:15: error: 'strlen' argument 1 declared
> attribute 'nonstring' [-Werror=stringop-overflow=]
>      s->size = strlen((char *)s->runstate) + 1;
>                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> GCC won... It is true this strlen() is buggy, indeed s->runstate might
> be not NUL-terminated.


Ooh nice. I smell some CVE fixes coming from this effort.


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MST