fix accidental corrdump

[Maxim Dounin]

Hello!

On Wed, Sep 28, 2022 at 10:56:15AM +0800, zjd wrote:

> my module is such:
> The pool is created with ngx_create_pool  in 
> module_init_process; I get momery from the pool in the start of 
> each request, and then use ngx_reset_pool in the end of  each 
> request.
> The ngx_reset_pool  take pool->large each alloc  pointer return 
> to pool, and each alloc pointer  is wild pointer.
>  And When  another  get momery from the pool  in next request or 
>  next next request..., I maybe get wild pointer address and 
>  access inaccessible addresses, and then coredump.
> 
> maybe  the describe is simple in last mail.

Ok, so from your description you are getting segfaults, and you 
don't know why.

Note that the ngx_reset_pool() function clears pool->large, and 
also frees all the ngx_pool_large_t structures (since it resets 
all pool blocks).  That is, l->alloc you are clearing in your 
patch is not expected to be used anywhere.  If clearing it helps, 
this suggests that there is a bug in your module which results in 
this freed memory to be used somehow.

While clearing l->alloc might appear to help, most likely it is 
just hiding a bug in your module.  Correct solution would be to 
find the bug in your module and fix it.

-- 
Maxim Dounin
http://mdounin.ru/