linux.git/fs/sysfs, branch v6.18.21

sysfs: check visibility before changing group attribute ownership

2025-10-17T07:48:34+00:00

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:
  
  ? 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
 [...]
  

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

Fixes: 303a42769c4c ("sysfs: add sysfs_group{s}_change_owner()")
Fixes: 0c17270f9b92 ("net: sysfs: Implement is_visible for phys_(port_id, port_name, switch_id)")
Reported-by: Cynthia 
Closes: https://lore.kernel.org/netdev/01070199e22de7f8-28f711ab-d3f1-46d9-b9a0-048ab05eb09b-000000@eu-central-1.amazonses.com/
Signed-off-by: Fernando Fernandez Mancera 
Reviewed-by: Jakub Kicinski 
Link: https://lore.kernel.org/r/20251016101456.4087-1-fmancera@suse.de
Signed-off-by: Greg Kroah-Hartman

sysfs: remove bin_attribute::read_new/write_new()

2025-08-19T11:12:12+00:00

These transitional fields are now unused and unnecessary.
Remove them and their logic in the sysfs core.

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20250811-sysfs-const-bin_attr-final-v4-1-7b6053fd58bb@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

sysfs: constify internal references to 'struct bin_attribute'

2025-06-17T08:44:09+00:00

The sysfs core handles 'const struct bin_attribute *'.

Adapt the internal references.

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20250530-sysfs-const-bin_attr-final-v3-2-724bfcf05b99@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

sysfs: constify attribute_group::bin_attrs

2025-04-15T16:46:10+00:00

All users of this field have been migrated to bin_attrs_new.
It can now be constified.

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20250313-sysfs-const-bin_attr-final-v2-2-96284e1e88ce@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

kernfs: Use RCU to access kernfs_node::name.

2025-02-15T16:46:32+00:00

Using RCU lifetime rules to access kernfs_node::name can avoid the
trouble with kernfs_rename_lock in kernfs_name() and kernfs_path_from_node()
if the fs was created with KERNFS_ROOT_INVARIANT_PARENT. This is usefull
as it allows to implement kernfs_path_from_node() only with RCU
protection and avoiding kernfs_rename_lock. The lock is only required if
the __parent node can be changed and the function requires an unchanged
hierarchy while it iterates from the node to its parent.
The change is needed to allow the lookup of the node's path
(kernfs_path_from_node()) from context which runs always with disabled
preemption and or interrutps even on PREEMPT_RT. The problem is that
kernfs_rename_lock becomes a sleeping lock on PREEMPT_RT.

I went through all ::name users and added the required access for the lookup
with a few extensions:
- rdtgroup_pseudo_lock_create() drops all locks and then uses the name
  later on. resctrl supports rename with different parents. Here I made
  a temporal copy of the name while it is used outside of the lock.

- kernfs_rename_ns() accepts NULL as new_parent. This simplifies
  sysfs_move_dir_ns() where it can set NULL in order to reuse the current
  name.

- kernfs_rename_ns() is only using kernfs_rename_lock if the parents are
  different. All users use either kernfs_rwsem (for stable path view) or
  just RCU for the lookup. The ::name uses always RCU free.

Use RCU lifetime guarantees to access kernfs_node::name.

Suggested-by: Tejun Heo 
Acked-by: Tejun Heo 
Reported-by: syzbot+6ea37e2e6ffccf41a7e6@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/67251dc6.050a0220.529b6.015e.GAE@google.com/
Reported-by: Hillf Danton 
Closes: https://lore.kernel.org/20241102001224.2789-1-hdanton@sina.com
Signed-off-by: Sebastian Andrzej Siewior 
Link: https://lore.kernel.org/r/20250213145023.2820193-7-bigeasy@linutronix.de
Signed-off-by: Greg Kroah-Hartman

kernfs: Use RCU to access kernfs_node::parent.

2025-02-15T16:46:32+00:00

kernfs_rename_lock is used to obtain stable kernfs_node::{name|parent}
pointer. This is a preparation to access kernfs_node::parent under RCU
and ensure that the pointer remains stable under the RCU lifetime
guarantees.

For a complete path, as it is done in kernfs_path_from_node(), the
kernfs_rename_lock is still required in order to obtain a stable parent
relationship while computing the relevant node depth. This must not
change while the nodes are inspected in order to build the path.
If the kernfs user never moves the nodes (changes the parent) then the
kernfs_rename_lock is not required and the RCU guarantees are
sufficient. This "restriction" can be set with
KERNFS_ROOT_INVARIANT_PARENT. Otherwise the lock is required.

Rename kernfs_node::parent to kernfs_node::__parent to denote the RCU
access and use RCU accessor while accessing the node.
Make cgroup use KERNFS_ROOT_INVARIANT_PARENT since the parent here can
not change.

Acked-by: Tejun Heo 
Cc: Yonghong Song 
Signed-off-by: Sebastian Andrzej Siewior 
Link: https://lore.kernel.org/r/20250213145023.2820193-6-bigeasy@linutronix.de
Signed-off-by: Greg Kroah-Hartman

sysfs: constify bin_attribute argument of sysfs_bin_attr_simple_read()

2025-01-09T09:43:58+00:00

Most users use this function through the BIN_ATTR_SIMPLE* macros,
they can handle the switch transparently.
Also adapt the two non-macro users in the same change.

Signed-off-by: Thomas Weißschuh 
Acked-by: Madhavan Srinivasan 
Reviewed-by: Mahesh Salgaonkar 
Tested-by: Aditya Gupta 
Link: https://lore.kernel.org/r/20241228-sysfs-const-bin_attr-simple-v2-1-7c6f3f1767a3@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

sysfs: bin_attribute: add const read/write callback variants

2024-11-05T13:00:28+00:00

To make it possible to put struct bin_attribute into read-only memory,
the sysfs core has to stop passing mutable pointers to the read() and
write() callbacks.
As there are numerous implementors of these callbacks throughout the
tree it's not possible to change all of them at once.
To enable a step-by-step transition, add new variants of the read() and
write() callbacks which differ only in the constness of the struct
bin_attribute argument.

As most binary attributes are defined through macros, extend these
macros to transparently handle both variants of callbacks to minimize
the churn during the transition.
As soon as all handlers are switch to the const variant, the non-const
one can be removed together with the transition machinery.

Signed-off-by: Thomas Weißschuh 
Acked-by: Krzysztof Wilczyński 
Link: https://lore.kernel.org/r/20241103-sysfs-const-bin_attr-v2-9-71110628844c@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

sysfs: introduce callback attribute_group::bin_size

2024-11-05T13:00:28+00:00

Several drivers need to dynamically calculate the size of an binary
attribute. Currently this is done by assigning attr->size from the
is_bin_visible() callback.

This has drawbacks:
* It is not documented.
* A single attribute can be instantiated multiple times, overwriting the
  shared size field.
* It prevents the structure to be moved to read-only memory.

Introduce a new dedicated callback to calculate the size of the
attribute.

Signed-off-by: Thomas Weißschuh 
Acked-by: Krzysztof Wilczyński 
Link: https://lore.kernel.org/r/20241103-sysfs-const-bin_attr-v2-2-71110628844c@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

sysfs: explicitly pass size to sysfs_add_bin_file_mode_ns()

2024-11-05T13:00:28+00:00

Upcoming changes to the sysfs core require the size of the created file
to be overridable by the caller.
Add a parameter to enable this.
For now keep using attr->size in all cases.

Signed-off-by: Thomas Weißschuh 
Acked-by: Krzysztof Wilczyński 
Link: https://lore.kernel.org/r/20241103-sysfs-const-bin_attr-v2-1-71110628844c@weissschuh.net
Signed-off-by: Greg Kroah-Hartman