[PATCH] net: core: prevent NULL deref in generic_hwtstamp_ioctl_lower()

[Jiaming Zhang]

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...@linux.dev/T/#mf5df538e21753e3045de98f25aa18d948be07df3
Signed-off-by: Jiaming Zhang <r7725...@gmail.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 */
+ 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 */
+ if (!kernel_cfg->ifr)
+ return -EOPNOTSUPP;
+
/* Legacy path: unconverted lower driver */
return generic_hwtstamp_ioctl_lower(dev, SIOCSHWTSTAMP, kernel_cfg);
}
--
2.34.1

[Kory Maincent]

nit: "lower driver", to be precise.

With this change:
Reviewed-by: Kory Maincent <kory.m...@bootlin.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

[Jiaming Zhang]

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...@linux.dev/T/#mf5df538e21753e3045de98f25aa18d948be07df3
Signed-off-by: Jiaming Zhang <r7725...@gmail.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..a32e1036f12a 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 lower driver */

+ 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 lower driver */

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

2.34.1

[Jiaming Zhang]

Hi Kory,

Apologies for the resubmission (v3); I forgot to add Reviewed-by tag in
the v2 patch.

v3:
- Add Kory's Reviewed-by tag.

v2:
- Fix typo in comment ("driver" -> "lower driver")

Best Regards,
Jiaming Zhang

Jiaming Zhang (1):
net: core: prevent NULL deref in generic_hwtstamp_ioctl_lower()

net/core/dev_ioctl.c | 8 ++++++++
1 file changed, 8 insertions(+)

--
2.34.1

[Jiaming Zhang]

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...@linux.dev/T/#mf5df538e21753e3045de98f25aa18d948be07df3
Signed-off-by: Jiaming Zhang <r7725...@gmail.com>

Reviewed-by: Kory Maincent <kory.m...@bootlin.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..a32e1036f12a 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 lower driver */

+ 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 lower driver */

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

2.34.1

[Jakub Kicinski]

On Thu, 30 Oct 2025 12:49:47 +0000 Jiaming Zhang wrote:
> + /* Netlink path with unconverted lower driver */
> + 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 lower driver */
> + if (!kernel_cfg->ifr)
> + return -EOPNOTSUPP;
> +
> /* Legacy path: unconverted lower driver */
> return generic_hwtstamp_ioctl_lower(dev, SIOCSHWTSTAMP, kernel_cfg);

Sorry but nit:

instead of adding this to both callers you can add the check in
generic_hwtstamp_ioctl_lower().
--
pw-bot: cr