PROBLEM: linux 2.6.13.4 (snapgear-3.3.0) scripts/mod/modpost dumps core

[Jeff Johnson <jellofan@gmail.com>]

I'm new at this, so hopefully this is OK.  I'm working on an embedded
system using snapgear-3.3.0 (linux 2.6.13.4).  The kernel build fails
when executing modpost -- it dumps core.  I have debugged the problem.
In modpost.c:buf_printf() appears the following code:
      len = vsnprintf(tmp, SZ, fmt, ap);
      if (buf->size - buf->pos < len + 1) {
          buf->size += 128;
          buf->p = realloc(buf->p, buf->size);
      }
      strncpy(buf->p + buf->pos, tmp, len + 1);

What I have discovered is that in my environment, in some cases the
output from vsnprintf() exceeds 128 characters.  So when the test for
"remaining space < len" fails, and the buf is realloc'ed, not enough
memory is allocated, and the subsequent strncpy overflows the buffer.

My solution was to change the assignment of buf->size as follows:
          buf->size += 128 * ((len/128)+1);

This will cause buf->size to increment by enough 128 byte blocks to
hold the string.  If it isn't important to increment in 128 byte
chunks, then I suppose you could just have:
          buf->size += SZ;

Thanks
Jeff