Bug#517714: glibc: possible signed integer overflow in libio/iogetdelim.c

[Jakub Wilk <ubanus@users.sf.net>]

Package: libc6
Version: 2.9-3
Severity: minor

An excerpt from gcc manual page:

  -fstrict-overflow

  Allow the compiler to assume strict signed overflow rules, depending 
  on the language being compiled. For C (and C++) this means that 
  overflow when doing arithmetic with signed numbers is undefined, which 
  means that the compiler may assume that it will not happen. 
  [...]
  When this option is in effect any attempt to determine whether an 
  operation on signed numbers will overflow must be written carefully to 
  not actually involve overflow.
  [...]
  The -fstrict-overflow option is enabled at levels -O2, -O3, -Os.

(Note that glibc is compiled with -O2 in Debian.)

I guess the following code snippet from libio/iogetdelim.c could serve 
as an example how *not* to write code, when this option is turned on:

  if (__builtin_expect (cur_len + len + 1 < 0, 0))
    {
      __set_errno (EOVERFLOW);
      result = -1;
      goto unlock_return;
    }

--
Jakub Wilk