Recursion in as_info_where

[Alan Modra]

On Fri, Feb 03, 2023 at 02:44:06PM +0100, Jan Beulich wrote:
> On 01.02.2023 12:59, Alan Modra wrote:
> > On Wed, Feb 01, 2023 at 10:24:25AM +0100, Jan Beulich wrote:
> >> On 01.02.2023 07:36, Alan Modra via Binutils wrote:
> >>> This function has a gas_assert, ie. possible call to as_abort, which
> >>> calls as_report_context, which calls as_info_where.  Attached fuzzer
> >>> testcase managed to trigger a stack overflow.
> >>>
> >>> 	* messages.c (as_info_where): Don't gas_assert.
> >>>
> >>> diff --git a/gas/messages.c b/gas/messages.c
> >>> index 0db075d779c..7c018acf69f 100644
> >>> --- a/gas/messages.c
> >>> +++ b/gas/messages.c
> >>> @@ -141,8 +141,6 @@ as_info_where (const char *file, unsigned int line, unsigned int indent,
> >>>    va_list args;
> >>>    char buffer[2000];
> >>>  
> >>> -  gas_assert (file != NULL && line > 0 && indent <= INT_MAX);
> >>
> >> If this go in the way, isn't it that the assertion actually triggered?
> >> In which case shouldn't the cause for it triggering be addressed
> >> instead, to avoid subsequent knock-on damage (e.g. from de-referencing
> >> "file"? (I may want to play with the testcase a little myself.)
> > 
> > The testcase is really weird, something that no programmer would ever
> > write.  It failed the assert with line == 0.  I'll let you discover
> > the horrible "# line file" with embedded \0 that gets you there.  :-)
> 
> Sure. That's an interaction bug between read_a_source_file()'s bumping
> of line numbers and s_linefile() trying to compensate. I have a fix for
> that, but I'll want to give it wider testing before posting.
> 
> As to the assertion here, I'd prefer if we would keep it, and do e.g.
> the below instead. Thoughts?

I think it is bad practice for a low-level error handling function to
assert.

-- 
Alan Modra
Australia Development Lab, IBM