sanitizer: crashes when flags contain GLOB_DOOFFS and offset is not null

[sthibaul]

Hello,

For instance, this:

#include <string.h>
#include <glob.h>
int main(void) {
  glob_t g;
  memset(&g, 0, sizeof(g));
  g.gl_offs = 1;
  glob("*", GLOB_DOOFFS, NULL, &g);
  return 0;
}

crashes with

AddressSanitizer:DEADLYSIGNAL
=================================================================
==2734336==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f9f1b93aec6 bp 0x7ffe664ee1a0 sp 0x7ffe664ed938 T0)
==2734336==The signal is caused by a READ memory access.
==2734336==Hint: address points to the zero page.
    #0 0x7f9f1b93aec6 in __sanitizer::internal_strlen(char const*) ../../../../src/libsanitizer/sanitizer_common/sanitizer_libc.cpp:176
    #1 0x7f9f1b89920f in unpoison_glob_t ../../../../src/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:2346
    #2 0x7f9f1b8ed26f in glob ../../../../src/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:2422
    #3 0x55e1afb552a0 in main (/home/samy/test+0x12a0) (BuildId: 6a2b7870466624765046114b28178ff268479b85)
    #4 0x7f9f1b633d67 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #5 0x7f9f1b633e24 in __libc_start_main_impl ../csu/libc-start.c:360
    #6 0x55e1afb550e0 in _start (/home/samy/test+0x10e0) (BuildId: 6a2b7870466624765046114b28178ff268479b85)

because libasan does not take care of GLOB_DOOFFS.

Something like the attached patch would be needed, I however don't know how libasan would cope with the OS-specific value of GLOB_DOOFFS

patch.txt