Heap corruption in win32 compiled by VC

Maxim Dounin mdounin at mdounin.ru
Wed Jul 13 14:58:49 MSD 2011


On Wed, Jul 13, 2011 at 01:36:38AM -0400, bigplum wrote:

> I checkout the newest code from svn and compiled it by vc, but an
> exception occurred. So I modified cl option to -MTd compiled again.
> The windbg shows that CheckBytes function return false when calling
> ngx_free() at ngx_shmem.c:43.
> I think that ngx_sprintf must put more than name's alloc size bytes into
> name, So I use ngx_snprintf to replace ngx_sprintf. The problem
> disappeared. Is it useful?
>     name = ngx_alloc(shm->name.len + 2 + sizeof(NGX_INT32_LEN),
> shm->log);
>     if (name == NULL) {
>         return NGX_ERROR;
>     }
> -    (void) ngx_sprintf(name, "%V_%s%Z", &shm->name, ngx_unique);
> +    (void) ngx_snprintf(name, shm->name.len + 2 +
> sizeof(NGX_INT32_LEN), 
> +                                    "%V_%s%Z", &shm->name, ngx_unique);

The fact that patch helps suggests that ngx_unique wasn't set 
properly.  Looks like ./configure problem for me.

(on the other hand, setting ngx_unique needs more sanity checking 
anyway: looks like it currently just trusts environment if it's 
found, not a good thing to do)

Maxim Dounin

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