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

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 (local)
Signed-off-by: Jiaming Zhang <redacted>
---
 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