linux-kernel - Re: [PATCH v3] fsi: Aspeed: Fix a potential double free

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Date:   Mon, 21 Feb 2022 09:24:22 +0000
From:   Joel Stanley <joel@....id.au>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Jeremy Kerr <jk@...abs.org>,
        Alistar Popple <alistair@...ple.id.au>,
        Eddie James <eajames@...ux.ibm.com>,
        Andrew Jeffery <andrew@...id.au>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Guenter Roeck <linux@...ck-us.net>, linux-fsi@...ts.ozlabs.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>
Subject: Re: [PATCH v3] fsi: Aspeed: Fix a potential double free

Hi Christophe,

Thanks for the patch.

On Sun, 9 Jan 2022 at 21:56, Christophe JAILLET
<christophe.jaillet@...adoo.fr> wrote:
>
> A struct device can never be devm_alloc()'ed.
> Here, it is embedded in "struct fsi_master", and "struct fsi_master" is
> embedded in "struct fsi_master_aspeed".
>
> Since "struct device" is embedded, the data structure embedding it must be
> released with the release function, as is already done here.
>
> So use kzalloc() instead of devm_kzalloc() when allocating "aspeed" and
> update all error handling branches accordingly.

This looks like a problem with the design of the fsi master structure.
It's a common pattern to devm_alloc the platform devices as they are
probed, the fsi masters all embed a copy of struct fsi_master, which
as you say embeds struct device.

Can we learn from other bus drivers (eg i2c?) how we should lay out
these structures?




>
> This prevent a potential double free().
>
> This also fix another issue if opb_readl() fails. Instead of a direct
> return, it now jumps in the error handling path.
>
> Fixes: 606397d67f41 ("fsi: Add ast2600 master driver")
> Suggested-by: Greg KH <gregkh@...uxfoundation.org>
> Suggested-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> v2: Keep the release function which is correct
>     s/devm_kzalloc()/kzalloc()/ instead
>
> v3: Update the error handling path to free "aspeed" [Guenter Roeck]
>     Fix another issue when opb_readl() fails [Guenter Roeck]
>
> I hope that fixing both issues in the same patch is ok. It makes no sense
> to me not to update the goto to the correct label if opb_readl() fails.
> ---
>  drivers/fsi/fsi-master-aspeed.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/fsi/fsi-master-aspeed.c b/drivers/fsi/fsi-master-aspeed.c
> index 8606e55c1721..0bed2fab8055 100644
> --- a/drivers/fsi/fsi-master-aspeed.c
> +++ b/drivers/fsi/fsi-master-aspeed.c
> @@ -542,25 +542,28 @@ static int fsi_master_aspeed_probe(struct platform_device *pdev)
>                 return rc;
>         }
>
> -       aspeed = devm_kzalloc(&pdev->dev, sizeof(*aspeed), GFP_KERNEL);
> +       aspeed = kzalloc(sizeof(*aspeed), GFP_KERNEL);
>         if (!aspeed)
>                 return -ENOMEM;
>
>         aspeed->dev = &pdev->dev;
>
>         aspeed->base = devm_platform_ioremap_resource(pdev, 0);
> -       if (IS_ERR(aspeed->base))
> -               return PTR_ERR(aspeed->base);
> +       if (IS_ERR(aspeed->base)) {
> +               rc = PTR_ERR(aspeed->base);
> +               goto err_free_aspeed;
> +       }
>
>         aspeed->clk = devm_clk_get(aspeed->dev, NULL);
>         if (IS_ERR(aspeed->clk)) {
>                 dev_err(aspeed->dev, "couldn't get clock\n");
> -               return PTR_ERR(aspeed->clk);
> +               rc = PTR_ERR(aspeed->clk);
> +               goto err_free_aspeed;
>         }
>         rc = clk_prepare_enable(aspeed->clk);
>         if (rc) {
>                 dev_err(aspeed->dev, "couldn't enable clock\n");
> -               return rc;
> +               goto err_free_aspeed;
>         }
>
>         rc = setup_cfam_reset(aspeed);
> @@ -595,7 +598,7 @@ static int fsi_master_aspeed_probe(struct platform_device *pdev)
>         rc = opb_readl(aspeed, ctrl_base + FSI_MVER, &raw);
>         if (rc) {
>                 dev_err(&pdev->dev, "failed to read hub version\n");
> -               return rc;
> +               goto err_release;
>         }
>
>         reg = be32_to_cpu(raw);
> @@ -634,6 +637,8 @@ static int fsi_master_aspeed_probe(struct platform_device *pdev)
>
>  err_release:
>         clk_disable_unprepare(aspeed->clk);
> +err_free_aspeed:
> +       kfree(aspeed);
>         return rc;
>  }
>
> --
> 2.32.0
>