netdev - Re: [PATCH] net: core: prevent NULL deref in generic_hwtstamp_ioctl

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Message-ID: <20251030111445.0fe0b313@kmaincent-XPS-13-7390>
Date: Thu, 30 Oct 2025 11:14:45 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Jiaming Zhang <r772577952@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org,
 kuba@...nel.org, kuniyu@...gle.com, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, pabeni@...hat.com, sdf@...ichev.me,
 syzkaller@...glegroups.com, vladimir.oltean@....com, stable@...r.kernel.org
Subject: Re: [PATCH] net: core: prevent NULL deref in
 generic_hwtstamp_ioctl_lower()

On Thu, 30 Oct 2025 09:36:21 +0000
Jiaming Zhang <r772577952@...il.com> wrote:

> The ethtool tsconfig Netlink path can trigger a null pointer
> dereference. A call chain such as:
> 
>   tsconfig_prepare_data() ->
>   dev_get_hwtstamp_phylib() ->
>   vlan_hwtstamp_get() ->
>   generic_hwtstamp_get_lower() ->
>   generic_hwtstamp_ioctl_lower()
> 
> results in generic_hwtstamp_ioctl_lower() being called with
> kernel_cfg->ifr as NULL.
> 
> The generic_hwtstamp_ioctl_lower() function does not expect a
> NULL ifr and dereferences it, leading to a system crash.
> 
> Fix this by adding a NULL check for kernel_cfg->ifr in
> generic_hwtstamp_get/set_lower(). If ifr is NULL, return
> -EOPNOTSUPP to prevent the call to the legacy IOCTL helper.
> 
> Fixes: 6e9e2eed4f39 ("net: ethtool: Add support for tsconfig command to
> get/set hwtstamp config") Closes:
> https://lore.kernel.org/lkml/cd6a7056-fa6d-43f8-b78a-f5e811247ba8@linux.dev/T/#mf5df538e21753e3045de98f25aa18d948be07df3
> Signed-off-by: Jiaming Zhang <r772577952@...il.com> ---
>  net/core/dev_ioctl.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
> index ad54b12d4b4c..39eaf6ba981a 100644
> --- a/net/core/dev_ioctl.c
> +++ b/net/core/dev_ioctl.c
> @@ -474,6 +474,10 @@ int generic_hwtstamp_get_lower(struct net_device *dev,
>  		return err;
>  	}
>  
> +	/* Netlink path with unconverted driver */

nit: "lower driver", to be precise.

With this change:
Reviewed-by: Kory Maincent <kory.maincent@...tlin.com>

Thank you!

> +	if (!kernel_cfg->ifr)
> +		return -EOPNOTSUPP;
> +
>  	/* Legacy path: unconverted lower driver */
>  	return generic_hwtstamp_ioctl_lower(dev, SIOCGHWTSTAMP, kernel_cfg);
>  }
> @@ -498,6 +502,10 @@ int generic_hwtstamp_set_lower(struct net_device *dev,
>  		return err;
>  	}
>  
> +	/* Netlink path with unconverted driver */

same.

> +	if (!kernel_cfg->ifr)
> +		return -EOPNOTSUPP;
> +
>  	/* Legacy path: unconverted lower driver */
>  	return generic_hwtstamp_ioctl_lower(dev, SIOCSHWTSTAMP, kernel_cfg);
>  }



-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com