linux-kernel - Re: [PATCH v2 net] net: phy: mscc: Add error check when __phy

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Date:   Tue, 10 May 2022 16:48:33 +0200
From:   Antoine Tenart <atenart@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Eric Dumazet <edumazet@...gle.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Wan Jiabing <wanjiabing@...o.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net] net: phy: mscc: Add error check when __phy_read() failed

Hello,

Quoting Wan Jiabing (2022-05-10 16:22:45)
> Calling __phy_read() might return a negative error code. Use 'int'
> to declare variables which call __phy_read() and also add error check
> for them.
> 
> The numerous callers of vsc8584_macsec_phy_read() don't expect it to
> fail. So don't return the error code from __phy_read(), but also don't
> return random values if it does fail.
> 
> Fixes: fa164e40c53b ("net: phy: mscc: split the driver into separate files")

Does this fix an actual issue or was this found by code inspection? If
that is not fixing a real issue I don't think it should go to stable
trees.

Also this is not the right commit, the __phy_read call was introduced
before splitting the file.

>  static u32 vsc8584_macsec_phy_read(struct phy_device *phydev,
>                                    enum macsec_bank bank, u32 reg)
>  {
> -       u32 val, val_l = 0, val_h = 0;
> +       int rc, val, val_l, val_h;
>         unsigned long deadline;
> -       int rc;
> +       u32 ret = 0;
>  
>         rc = phy_select_page(phydev, MSCC_PHY_PAGE_MACSEC);
>         if (rc < 0)
> @@ -47,15 +47,20 @@ static u32 vsc8584_macsec_phy_read(struct phy_device *phydev,
>         deadline = jiffies + msecs_to_jiffies(PROC_CMD_NCOMPLETED_TIMEOUT_MS);
>         do {
>                 val = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_19);
> +               if (val < 0)
> +                       goto failed;
>         } while (time_before(jiffies, deadline) && !(val & MSCC_PHY_MACSEC_19_CMD));
>  
>         val_l = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_17);
>         val_h = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_18);
>  
> +       if (val_l > 0 && val_h > 0)
> +               ret = (val_h << 16) | val_l;

Both values have to be non-0 for the function to return a value? I
haven't checked but I would assume it is valid to have one of the two
being 0.

>  failed:
>         phy_restore_page(phydev, rc, rc);
>  
> -       return (val_h << 16) | val_l;
> +       return ret;
>  }

Thanks,
Antoine