linux-kernel - [PATCH] sysfs: check visibility before changing group attribute ownership

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Message-ID: <20251016101456.4087-1-fmancera@suse.de>
Date: Thu, 16 Oct 2025 12:14:56 +0200
From: Fernando Fernandez Mancera <fmancera@...e.de>
To: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org,
	kuba@...nel.org
Cc: cynthia@...mx.dev,
	rafael@...nel.org,
	dakr@...nel.org,
	christian.brauner@...ntu.com,
	edumazet@...gle.com,
	pabeni@...hat.com,
	davem@...emloft.net,
	horms@...nel.org,
	Fernando Fernandez Mancera <fmancera@...e.de>
Subject: [PATCH] sysfs: check visibility before changing group attribute ownership

Since commit 0c17270f9b92 ("net: sysfs: Implement is_visible for
phys_(port_id, port_name, switch_id)"), __dev_change_net_namespace() can
hit WARN_ON() when trying to change owner of a file that isn't visible.
See the trace below:

 WARNING: CPU: 6 PID: 2938 at net/core/dev.c:12410 __dev_change_net_namespace+0xb89/0xc30
 CPU: 6 UID: 0 PID: 2938 Comm: incusd Not tainted 6.17.1-1-mainline #1 PREEMPT(full)  4b783b4a638669fb644857f484487d17cb45ed1f
 Hardware name: Framework Laptop 13 (AMD Ryzen 7040Series)/FRANMDCP07, BIOS 03.07 02/19/2025
 RIP: 0010:__dev_change_net_namespace+0xb89/0xc30
 [...]
 Call Trace:
  <TASK>
  ? if6_seq_show+0x30/0x50
  do_setlink.isra.0+0xc7/0x1270
  ? __nla_validate_parse+0x5c/0xcc0
  ? security_capable+0x94/0x1a0
  rtnl_newlink+0x858/0xc20
  ? update_curr+0x8e/0x1c0
  ? update_entity_lag+0x71/0x80
  ? sched_balance_newidle+0x358/0x450
  ? psi_task_switch+0x113/0x2a0
  ? __pfx_rtnl_newlink+0x10/0x10
  rtnetlink_rcv_msg+0x346/0x3e0
  ? sched_clock+0x10/0x30
  ? __pfx_rtnetlink_rcv_msg+0x10/0x10
  netlink_rcv_skb+0x59/0x110
  netlink_unicast+0x285/0x3c0
  ? __alloc_skb+0xdb/0x1a0
  netlink_sendmsg+0x20d/0x430
  ____sys_sendmsg+0x39f/0x3d0
  ? import_iovec+0x2f/0x40
  ___sys_sendmsg+0x99/0xe0
  __sys_sendmsg+0x8a/0xf0
  do_syscall_64+0x81/0x970
  ? __sys_bind+0xe3/0x110
  ? syscall_exit_work+0x143/0x1b0
  ? do_syscall_64+0x244/0x970
  ? sock_alloc_file+0x63/0xc0
  ? syscall_exit_work+0x143/0x1b0
  ? do_syscall_64+0x244/0x970
  ? alloc_fd+0x12e/0x190
  ? put_unused_fd+0x2a/0x70
  ? do_sys_openat2+0xa2/0xe0
  ? syscall_exit_work+0x143/0x1b0
  ? do_syscall_64+0x244/0x970
  ? exc_page_fault+0x7e/0x1a0
  entry_SYSCALL_64_after_hwframe+0x76/0x7e
 [...]
  </TASK>

Fix this by checking is_visible() before trying to touch the attribute.

Fixes: 303a42769c4c ("sysfs: add sysfs_group{s}_change_owner()")
Reported-by: Cynthia <cynthia@...mx.dev>
Closes: https://lore.kernel.org/netdev/01070199e22de7f8-28f711ab-d3f1-46d9-b9a0-048ab05eb09b-000000@eu-central-1.amazonses.com/
Signed-off-by: Fernando Fernandez Mancera <fmancera@...e.de>
---
 fs/sysfs/group.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 2d78e94072a0..e142bac4f9f8 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -498,17 +498,26 @@ int compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
 }
 EXPORT_SYMBOL_GPL(compat_only_sysfs_link_entry_to_kobj);
 
-static int sysfs_group_attrs_change_owner(struct kernfs_node *grp_kn,
+static int sysfs_group_attrs_change_owner(struct kobject *kobj,
+					  struct kernfs_node *grp_kn,
 					  const struct attribute_group *grp,
 					  struct iattr *newattrs)
 {
 	struct kernfs_node *kn;
-	int error;
+	int error, i;
+	umode_t mode;
 
 	if (grp->attrs) {
 		struct attribute *const *attr;
 
-		for (attr = grp->attrs; *attr; attr++) {
+		for (i = 0, attr = grp->attrs; *attr; i++, attr++) {
+			if (grp->is_visible) {
+				mode = grp->is_visible(kobj, *attr, i);
+				if (mode & SYSFS_GROUP_INVISIBLE)
+					break;
+				if (!mode)
+					continue;
+			}
 			kn = kernfs_find_and_get(grp_kn, (*attr)->name);
 			if (!kn)
 				return -ENOENT;
@@ -523,7 +532,14 @@ static int sysfs_group_attrs_change_owner(struct kernfs_node *grp_kn,
 	if (grp->bin_attrs) {
 		const struct bin_attribute *const *bin_attr;
 
-		for (bin_attr = grp->bin_attrs; *bin_attr; bin_attr++) {
+		for (i = 0, bin_attr = grp->bin_attrs; *bin_attr; i++, bin_attr++) {
+			if (grp->is_bin_visible) {
+				mode = grp->is_bin_visible(kobj, *bin_attr, i);
+				if (mode & SYSFS_GROUP_INVISIBLE)
+					break;
+				if (!mode)
+					continue;
+			}
 			kn = kernfs_find_and_get(grp_kn, (*bin_attr)->attr.name);
 			if (!kn)
 				return -ENOENT;
@@ -573,7 +589,7 @@ int sysfs_group_change_owner(struct kobject *kobj,
 
 	error = kernfs_setattr(grp_kn, &newattrs);
 	if (!error)
-		error = sysfs_group_attrs_change_owner(grp_kn, grp, &newattrs);
+		error = sysfs_group_attrs_change_owner(kobj, grp_kn, grp, &newattrs);
 
 	kernfs_put(grp_kn);
 
-- 
2.51.0