linux-kernel - Re: Coverity: zblock_alloc(): Memory

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Date:   Fri, 18 Nov 2022 16:05:36 +0300
From:   Ananda Badmaev <a.badmaev@...cknet.pro>
To:     coverity-bot <keescook@...omium.org>
Cc:     Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-mm@...ck.org, linux-doc@...r.kernel.org,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-next@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: Coverity: zblock_alloc(): Memory - illegal accesses

18.11.2022 01:20, coverity-bot пишет:
> Coverity reported the following:
> 
> *** CID 1527352:  Memory - illegal accesses  (OVERRUN)
> mm/zblock.c:320 in zblock_alloc()
> 314     	}
> 315     	list = &(pool->block_lists[block_type]);
> 316
> 317     check:
> 318     	spin_lock(&list->lock);
> 319     	/* check if there are free slots in cache */
> vvv     CID 1527352:  Memory - illegal accesses  (OVERRUN)
> vvv     Overrunning array of 10208 bytes at byte offset 10208 by dereferencing pointer "list".
> 320     	block = cache_find_block(list);
> 321     	if (block)
> 322     		goto found;
> 323     	spin_unlock(&list->lock);
> 324
> 325     	/* not found block with free slots try to allocate new empty block */
> 
> If this is a false positive, please let us know so we can mark it as
> such, or teach the Coverity rules to be smarter. If not, please make
> sure fixes get into linux-next. :) For patches fixing this, please
> include these lines (but double-check the "Fixes" first):
> 
> Reported-by: coverity-bot <keescook+coverity-bot@...omium.org>
> Addresses-Coverity-ID: 1527352 ("Memory - illegal accesses")
> Fixes: 9097e28c25c8 ("mm: add zblock - new allocator for use via zpool API")
> 
> It looks like block_type is not checked to be < ARRAY_SIZE(block_desc)
> after exiting the earlier loop, so the access through "list" may be past
> the end of pool->block_lists.
>

There is no need for this check because it is guaranteed that this code 
will be executed only if size <= PAGE_SIZE. Since slot_size for the last 
list even exceeds PAGE_SIZE, block_type will be always valid.