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Subject回复: [PATCH] driver/ata: fix potential nul l pointer dereference on pointer last sge
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Got it. Thanks for your reply in such detail.

Best Regards,
Chengfeng

-----邮件原件-----
发件人: Damien Le Moal <damien.lemoal@opensource.wdc.com>
发送时间: 2021年10月26日 12:10
收件人: YE Chengfeng <cyeaa@connect.ust.hk>
抄送: linux-kernel@vger.kernel.org
主题: Re: [PATCH] driver/ata: fix potential null pointer dereference on pointer last_sge

On 2021/10/25 22:13, Chengfeng Ye wrote:
> The pointer cs_desc could be null if the loop is not executed, so
> there is a potential NULL-PTR dereference issue. Fix this by adding a
> null check before dereference.
>
> Signed-off-by: Chengfeng Ye <cyeaa@connect.ust.hk>
> ---
> drivers/ata/sata_sil24.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c index
> 06a1e27c4f84..2bd595da799f 100644
> --- a/drivers/ata/sata_sil24.c
> +++ b/drivers/ata/sata_sil24.c
> @@ -785,6 +785,8 @@ static inline void sil24_fill_sg(struct ata_queued_cmd *qc,
> sge++;
> }
>
> + if (!last_sge)
> + return;
> last_sge->flags = cpu_to_le32(SGE_TRM); }

I do not think that this fix is necessary: sil24_fill_sg() is called only if the qc has ATA_QCFLAG_DMAMAP set (see sil24_qc_prep()) and that in turn is only set if ata_sg_setup() sees at least one sg entry. So the loop in sil24_fill_sg() will always be executed for qc marked with ATA_QCFLAG_DMAMAP and so last_sg cannot be NULL.

--
Damien Le Moal
Western Digital Research
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