Re: Fix iogetdelim.c (latent) integer overflow (bug 9914)

[Andreas Jaeger <aj at suse dot com>]

On Monday, September 03, 2012 22:36:04 Joseph S. Myers wrote:
> Bug 9914 reports libio/iogetdelim.c wrongly trying to detect integer
> overflow after the event by seeing whether the result of an addition
> of positive values is negative, so resulting in the check potentially
> being optimized away.  This patch fixes this in the way described in a
> comment in the bug.  No testcase is added; I believe the bug is in
> fact latent (that the compiler won't be able to deduce that the
> 
>   len = fp->_IO_read_end - fp->_IO_read_ptr;
>   if (len <= 0)
>     {
>       if (__underflow (fp) == EOF)
>         {
>           result = -1;
>           goto unlock_return;
>         }
>       len = fp->_IO_read_end - fp->_IO_read_ptr;
>     }
> 
> code does not result in a negative value of len that is still live at
> this point).
> 
> (Note: I'm assuming that _IO_ssize_t always has the same limits as
> ssize_t.  _IO_ssize_t is defined to _G_ssize_t and it's indeed the
> case that all versions of _G_config.h do define that to __ssize_t.
> Given that libio is nowadays only used as part of glibc - it hasn't
> been used in libstdc++ for many years - I'm doubtful that most of the
> _G_config.h abstractions make sense any more and think some of the
> internal layers of types and macros in libio could reasonably be
> cleaned up.  The only difference between the two versions of
> _G_config.h that are actually used by current ports -
> sysdeps/gnu/_G_config.h and sysdeps/mach/hurd/_G_config.h - is that
> Hurd doesn't have mremap.)
> 
> Tested x86_64.
> 
> 2012-09-03  Joseph Myers  <joseph@codesourcery.com>
> 
> 	[BZ #9914]
> 	* libio/iogetdelim.c: Include <limits.h>.
> 	(_IO_getdelim): Avoid integer overflow in testing whether cur_len
> 	+ len + 1 would overflow.

Thanks, this is fine,

Andreas
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