linux-kernel - Re: [PATCH] crypto: af_alg - check possible NULL pointer

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Date:   Thu, 30 Dec 2021 16:57:40 -0600
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: af_alg - check possible NULL pointer

On Wed, Dec 29, 2021 at 05:32:16PM +0800, Jiasheng Jiang wrote:
> And then it will cause the BUG_ON() in sg_assign_page().

That's not true.  The two BUG_ON()'s in sg_assign_page() are:

        BUG_ON((unsigned long) page & (SG_CHAIN | SG_END));
#ifdef CONFIG_DEBUG_SG
        BUG_ON(sg_is_chain(sg));
#endif

Neither will trigger due to page == NULL.

>  		do {
> +			struct page *pg;
>  			unsigned int i = sgl->cur;
>  
>  			plen = min_t(size_t, len, PAGE_SIZE);
>  
> -			sg_assign_page(sg + i, alloc_page(GFP_KERNEL));
> +			pg = alloc_page(GFP_KERNEL);
> +			if (!pg) {
> +				err = -ENOMEM;
> +				goto unlock;
> +			}
> +
> +			sg_assign_page(sg + i, pg);
>  			if (!sg_page(sg + i)) {
>  				err = -ENOMEM;
>  				goto unlock;

The NULL check is already done, just below the redundant one you're adding.

I do think it would be more logical to do the NULL check before
sg_assign_page().  So you could send a patch that moves it there.  But it would
be a cleanup, not a fix.

- Eric