答复: Re: [PATCH 2/4] soc/fsl/qe: fix potential NULL pointer dereference inucc_of_parse_tdm

[wen.yang99 at zte.com.cn]

Hi Christophe, thank you for your review.
There are two problems in the ucc_of_parse_tdm function.
1, NULL pointer reference
2, pdev gets modified, iomap was done with a different pdev.

We will submit a patch to repair it later.
Thanks.

132         pdev = of_find_device_by_node(np2);
......
141         utdm->si_regs = devm_ioremap_resource(&pdev->dev, res);   ---> use pdev to call  devm_ioremap 
......
153         pdev = of_find_device_by_node(np2);   --->This line, pdev gets modified  
154         if (!pdev) {
155                 ret = -EINVAL;
156                 pr_err("%pOFn: failed to lookup pdev\n", np2);
157                 of_node_put(np2);
158                 goto err_miss_siram_property;                         ------> This line, if pdev is NULL, will jump to label err_miss_siram_property
159         }
......
163         utdm->siram = devm_ioremap_resource(&pdev->dev, res);  --> use  changed pdev to call devm_ioremap 
......
175 
176 err_miss_siram_property:
177         devm_iounmap(&pdev->dev, utdm->si_regs);    ------> Within the code block,  if pdev is NULL,  kernel panic will be triggered; devm_iounmap() will alse fail even when the new pdev is valid.
178         return ret;
179 }


------------------原始邮件------------------
发件人：ChristopheLEROY <christophe.leroy at c-s.fr>
收件人：文洋10156314;qiang.zhao at nxp.com <qiang.zhao at nxp.com>
抄送人：汪翼10129963;钟卫东10001088;linux-kernel at vger.kernel.org <linux-kernel at vger.kernel.org>leoyang.li at nxp.com <leoyang.li at nxp.com>Julia Lawall <julia.lawall at lip6.fr>linuxppc-dev at lists.ozlabs.org <linuxppc-dev at lists.ozlabs.org>linux-arm-kernel at lists.infradead.org <linux-arm-kernel at lists.infradead.org>
日 期 ：2018年11月21日 18:46
主 题 ：Re: [PATCH 2/4] soc/fsl/qe: fix potential NULL pointer dereference inucc_of_parse_tdm


Le 21/11/2018 à 08:41, Wen Yang a écrit :
> This patch fixes a possible null pointer dereference in
> ucc_of_parse_tdm, detected by the semantic patch
> deref_null.cocci, with the following warning:
>
> ./drivers/soc/fsl/qe/qe_tdm.c:177:21-24: ERROR: pdev is NULL but dereferenced.
>
> The following code has potential null pointer references:
>          pdev = of_find_device_by_node(np2);
>          if (!pdev) {
>                  ret = -EINVAL;
>                  pr_err("%pOFn: failed to lookup pdev\n", np2);
>                  of_node_put(np2);
>                  goto err_miss_siram_property;
>          }
> ...
> err_miss_siram_property:
>          devm_iounmap(&pdev->dev, utdm->si_regs);
>
> Signed-off-by: Wen Yang <wen.yang99 at zte.com.cn>
> Reviewed-by: Tan Hu <tan.hu at zte.com.cn>
> CC: Julia Lawall <julia.lawall at lip6.fr>
> ---
>   drivers/soc/fsl/qe/qe_tdm.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/soc/fsl/qe/qe_tdm.c b/drivers/soc/fsl/qe/qe_tdm.c
> index f78c346..166378b 100644
> --- a/drivers/soc/fsl/qe/qe_tdm.c
> +++ b/drivers/soc/fsl/qe/qe_tdm.c
> @@ -174,7 +174,8 @@ int ucc_of_parse_tdm(struct device_node *np, struct ucc_tdm *utdm,
>       return ret;
>
>   err_miss_siram_property:
> -    devm_iounmap(&pdev->dev, utdm->si_regs);
> +    if (pdev)
> +        devm_iounmap(&pdev->dev, utdm->si_regs);

You are just hiding the issue, not fixing it.

The problem is that pdev gets modified, so in any case that
devm_iounmap() will fail even when the new pdev is valid, because the
iomap was done with a different pdev.

Christophe



>       return ret;
>   }
>   EXPORT_SYMBOL(ucc_of_parse_tdm);
>