Re: Re: [PATCH v2] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE
From: Maurizio Lombardi <hidden>
Date: 2022-07-08 08:07:10
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st 1. 6. 2022 v 14:49 odesílatel 愚树 [off-list ref] napsal:
quoted hunk ↗ jump to hunk
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