Re: Crash with "ata: ahci_platform: convert kcalloc to devm_kcalloc"

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On Mon, Jul 16, 2018 at 06:33:52PM +0300, Mikko Perttunen wrote:
> 
> 
> On 07/16/2018 05:55 PM, LABBE Corentin wrote:
> > On Mon, Jul 16, 2018 at 04:11:44PM +0300, Mikko Perttunen wrote:
> >> Hello,
> >>
> >> the recently applied "ata: ahci_platform: convert kcalloc to
> >> devm_kcalloc" seems to be causing boot failures on Tegra124 Jetson TK1.
> >> The patch is as follows:
> >>
> >> diff --git a/drivers/ata/libahci_platform.c b/drivers/ata/libahci_platform.c
> >> index be9f54423a9b..fe8939e161ea 100644
> >> --- a/drivers/ata/libahci_platform.c
> >> +++ b/drivers/ata/libahci_platform.c
> >> @@ -271,8 +271,6 @@ static void ahci_platform_put_resources(struct
> >> device *dev, void *res)
> >>           for (c = 0; c < hpriv->nports; c++)
> >>                   if (hpriv->target_pwrs && hpriv->target_pwrs[c])
> >>                           regulator_put(hpriv->target_pwrs[c]);
> >> -
> >> -       kfree(hpriv->target_pwrs);
> >>    }
> >>
> >>    static int ahci_platform_get_phy(struct ahci_host_priv *hpriv, u32 port,
> >> @@ -408,7 +406,7 @@ struct ahci_host_priv
> >> *ahci_platform_get_resources(struct platform_device *pdev)
> >>                   rc = -ENOMEM;
> >>                   goto err_out;
> >>           }
> >> -       hpriv->target_pwrs = kcalloc(hpriv->nports,
> >> sizeof(*hpriv->target_pwrs), GFP_KERNEL);
> >> +       hpriv->target_pwrs = devm_kcalloc(dev, hpriv->nports,
> >> sizeof(*hpriv->target_pwrs), GFP_KERNEL);
> >>           if (!hpriv->target_pwrs) {
> >>                   rc = -ENOMEM;
> >>                   goto err_out;
> >>
> >> However, this is not valid, as it will cause hpriv->target_pwrs to be
> >> freed before ahci_platform_put_resources is called. With the older code,
> >> the free happened intentionally only after the regulator_put calls were
> >> done.
> >>
> > 
> > Hello
> > 
> > I am surprised, since I have tested all my AHCI patch on a Tegra124 Jetson TK1.
> > Could you print the boot crash ?
> 
> I don't have the crash log in front of me now (can get it to you 
> tomorrow), but basically it was ahci_platform_put_resources calling 
> eventually _regulator_put which was dereferencing 0x6b6b6bbf, quite 
> clearly an offset of 0x6b6b6b6b which is the use-after-free poison.
> 
> It actually only happens on tegra_defconfig -- I assume there's some 
> different dependency situation that doesn't happen on 
> multi_v7_defconfig, that causes ahci-tegra to defer probe, causing the 
> error path to be triggered.
> 

I have just checked on kernelci.org, and see what you said.
And yes it was the PHY defer which cause this, and explains why I didnt hit the case (I was not using defconfig).

I will send a commit that revert the change add add a warning on why it must remains a simple kcalloc.

Thanks
Regards
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