linux-kernel - Re: [PATCH 1/1] lib: scatterlist: Fix SGL length in sg_split() if !CONFIG_NEED_SG_DMA

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Message-ID: <20210419092325.GA3215674@infradead.org>
Date:   Mon, 19 Apr 2021 10:23:25 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Alexander Egorenkov <egorenar-dev@...teo.net>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] lib: scatterlist: Fix SGL length in sg_split() if
 !CONFIG_NEED_SG_DMA_LENGTH

On Sun, Apr 18, 2021 at 08:14:41AM +0000, Alexander Egorenkov wrote:
> If CONFIG_NEED_SG_DMA_LENGTH is NOT enabled then sg_dma_len() is an alias
> for the length field in a SGL. In that case sg_split() wrongly resets
> the length of split SGLs to zero after it was set correctly before.

Why is this routine messing with sg_dma_address and
sg_dma_lensg_dma_lensg_dma_len at all?  This whole sg_spli() routine
seems rather dangerous because ownership and state of the DMA mapping is
entirely unclear.