net: ethtool: fix NULL pointer dereference in phy_reply_size

In phy_prepare_data(), several strings such as 'name', 'drvname',
'upstream_sfp_name', and 'downstream_sfp_name' are allocated using
kstrdup(). However, these allocations were not checked  for failure.

If kstrdup() fails for 'name', it returns NULL while the function
continues. This leads to a kernel NULL pointer dereference and panic
later in phy_reply_size() when it unconditionally calls strlen() on
the NULL pointer.

While other strings like 'upstream_sfp_name' might be checked before
access in certain code paths, failing to handle these allocations
consistently can lead to incomplete data reporting or hidden bugs.

Fix this by adding proper NULL checks for all kstrdup() calls in
phy_prepare_data() and implement a centralized error handling path
using goto labels to ensure all previously allocated resources are
freed on failure.

Fixes: 9dd2ad5e92b9 ("net: ethtool: phy: Convert the PHY_GET command to generic phy dump")
Signed-off-by: Quan Sun <2022090917019@std.uestc.edu.cn>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260507131738.1173835-1-2022090917019@std.uestc.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ethtool/phy.c b/net/ethtool/phy.c
index d4e6887055ab15d63331e4c8d6d872286580bf29..f76d94d848d6da14bbb5da267f13890c2819d7e1 100644 (file)
--- a/net/ethtool/phy.c
+++ b/net/ethtool/phy.c
@@ -76,6 +76,7 @@ static int phy_prepare_data(const struct ethnl_req_info *req_info,
        struct nlattr **tb = info->attrs;
        struct phy_device_node *pdn;
        struct phy_device *phydev;
+       int ret;
 
        /* RTNL is held by the caller */
        phydev = ethnl_req_get_phydev(req_info, tb, ETHTOOL_A_PHY_HEADER,
@@ -88,8 +89,17 @@ static int phy_prepare_data(const struct ethnl_req_info *req_info,
                return -EOPNOTSUPP;
 
        rep_data->phyindex = phydev->phyindex;
+
        rep_data->name = kstrdup(dev_name(&phydev->mdio.dev), GFP_KERNEL);
+       if (!rep_data->name)
+               return -ENOMEM;
+
        rep_data->drvname = kstrdup(phydev->drv->name, GFP_KERNEL);
+       if (!rep_data->drvname) {
+               ret = -ENOMEM;
+               goto err_free_name;
+       }
+
        rep_data->upstream_type = pdn->upstream_type;
 
        if (pdn->upstream_type == PHY_UPSTREAM_PHY) {
@@ -97,15 +107,33 @@ static int phy_prepare_data(const struct ethnl_req_info *req_info,
                rep_data->upstream_index = upstream->phyindex;
        }
 
-       if (pdn->parent_sfp_bus)
+       if (pdn->parent_sfp_bus) {
                rep_data->upstream_sfp_name = kstrdup(sfp_get_name(pdn->parent_sfp_bus),
                                                      GFP_KERNEL);
+               if (!rep_data->upstream_sfp_name) {
+                       ret = -ENOMEM;
+                       goto err_free_drvname;
+               }
+       }
 
-       if (phydev->sfp_bus)
+       if (phydev->sfp_bus) {
                rep_data->downstream_sfp_name = kstrdup(sfp_get_name(phydev->sfp_bus),
                                                        GFP_KERNEL);
+               if (!rep_data->downstream_sfp_name) {
+                       ret = -ENOMEM;
+                       goto err_free_upstream_sfp;
+               }
+       }
 
        return 0;
+
+err_free_upstream_sfp:
+       kfree(rep_data->upstream_sfp_name);
+err_free_drvname:
+       kfree(rep_data->drvname);
+err_free_name:
+       kfree(rep_data->name);
+       return ret;
 }
 
 static int phy_fill_reply(struct sk_buff *skb,