Re: Re: [PATCH v2] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE

[Maurizio Lombardi <mlombard@redhat.com>]

st 1. 6. 2022 v 14:49 odesílatel 愚树 <chen45464546@163.com> napsal:
> Can we just add code to the relatively slow path to capture the mistake
> before it lead to memory corruption?
> Like:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e6f211d..ac60a97 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5580,6 +5580,7 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
>                 /* reset page count bias and offset to start of new frag */
>                 nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
>                 offset = size - fragsz;
> +               BUG_ON(offset < 0);
>         }
>

Personally, I'm not really convinced this is the best solution.
The next time a driver abuses  the page_frag_alloc() interface, the
bug may go unnoticed for a long time...
until a server in production runs into OOM and crashes because it hits
the BUG_ON().

And why should the kernel panic? It's perfectly able to handle this
condition by failing
the allocation and returning NULL, and printing a warning maybe.

Maurizio