The following code does not work anymore on glibc 2.7, while it was working on 
glibc 2.6:

#include <stdio.h>

int main()
{
  char *buf = " ";
  char *str;

  sscanf (buf, "%as", &str);
  printf("%p\n", str);
  return 0;
}


Instead the glibc now reports an invalid pointer:

*** glibc detected *** ./test: munmap_chunk(): invalid pointer: 
0x00007fffe37dd8c0 ***
======= Backtrace: =========
/lib/libc.so.6(cfree+0x1b6)[0x2b8ac7560d06]
/lib/libc.so.6(_IO_vfscanf+0x239f)[0x2b8ac753e29f]
/lib/libc.so.6(vsscanf+0x75)[0x2b8ac754ec85]
/lib/libc.so.6(_IO_sscanf+0x88)[0x2b8ac75498b8]
./test[0x4004bf]
/lib/libc.so.6(__libc_start_main+0xf4)[0x2b8ac75071c4]
./test[0x400409]
======= Memory map: ========
00400000-00401000 r-xp 00000000 08:02 
2392545                            /tmp/test
00600000-00601000 rw-p 00000000 08:02 
2392545                            /tmp/test
00601000-00622000 rw-p 00601000 00:00 0                                  [heap]
2b8ac72cb000-2b8ac72e8000 r-xp 00000000 08:02 
6669895                    /lib/ld-2.7.so
2b8ac72e8000-2b8ac72eb000 rw-p 2b8ac72e8000 00:00 0
2b8ac74e7000-2b8ac74e9000 rw-p 0001c000 08:02 
6669895                    /lib/ld-2.7.so
2b8ac74e9000-2b8ac763d000 r-xp 00000000 08:02 
6669873                    /lib/libc-2.7.so
2b8ac763d000-2b8ac783d000 ---p 00154000 08:02 
6669873                    /lib/libc-2.7.so
2b8ac783d000-2b8ac7840000 r--p 00154000 08:02 
6669873                    /lib/libc-2.7.so
2b8ac7840000-2b8ac7842000 rw-p 00157000 08:02 
6669873                    /lib/libc-2.7.so
2b8ac7842000-2b8ac7848000 rw-p 2b8ac7842000 00:00 0
2b8ac7848000-2b8ac7855000 r-xp 00000000 08:02 
21217454                   /lib/libgcc_s.so.1
2b8ac7855000-2b8ac7a55000 ---p 0000d000 08:02 
21217454                   /lib/libgcc_s.so.1
2b8ac7a55000-2b8ac7a56000 rw-p 0000d000 08:02 
21217454                   /lib/libgcc_s.so.1
7fffe37ca000-7fffe37df000 rw-p 7fffe37ca000 00:00 0                      
[stack]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vdso]