[PATCH v4 1/1] net: core: prevent NULL deref in generic_hwtstamp_ioctl_lower()

[Jiaming Zhang <r772577952@gmail.com>]

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_ioctl_lower(). If ifr is NULL, return -EINVAL.

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@gmail.com>
---
 net/core/dev_ioctl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index ad54b12d4b4c..8bb71a10dba0 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -443,6 +443,9 @@ static int generic_hwtstamp_ioctl_lower(struct net_device *dev, int cmd,
 	struct ifreq ifrr;
 	int err;
 
+	if (!kernel_cfg->ifr)
+		return -EINVAL;
+
 	strscpy_pad(ifrr.ifr_name, dev->name, IFNAMSIZ);
 	ifrr.ifr_ifru = kernel_cfg->ifr->ifr_ifru;
 
-- 
2.34.1