kernel/linux.git/include/linux/exportfs.h, branch v6.19.11

nfsd: do not allow exporting of special kernel filesystems

2026-02-26T23:01:26+00:00

[ Upstream commit b3c78bc53630d14a5770451ede3a30e7052f3b8b ] pidfs and nsfs recently gained support for encode/decode of file handles via name_to_handle_at(2)/open_by_handle_at(2). These special kernel filesystems have custom ->open() and ->permission() export methods, which nfsd does not respect and it was never meant to be used for exporting those filesystems by nfsd. Therefore, do not allow nfsd to export filesystems with custom ->open() or ->permission() methods. Fixes: b3caba8f7a34a ("pidfs: implement file handle support") Fixes: 5222470b2fbb3 ("nsfs: support file handles") Reviewed-by: Jeff Layton Signed-off-by: Amir Goldstein Link: https://patch.msgid.link/20260129100212.49727-3-amir73il@gmail.com Reviewed-by: Chuck Lever Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin

expfs: Fix exportfs_can_encode_fh() for EXPORT_FH_FID

2025-10-06T12:26:50+00:00

After commit 5402c4d4d200 ("exportfs: require ->fh_to_parent() to encode connectable file handles") we will fail to create non-decodable file handles for filesystems without export operations. Fix it. Fixes: 5402c4d4d200 ("exportfs: require ->fh_to_parent() to encode connectable file handles") Reviewed-by: Christian Brauner Reviewed-by: Amir Goldstein Signed-off-by: Jan Kara

Merge tag 'pull-f_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2025-10-03T23:32:36+00:00

Pull file->f_path constification from Al Viro: "Only one thing was modifying ->f_path of an opened file - acct(2). Massaging that away and constifying a bunch of struct path * arguments in functions that might be given &file->f_path ends up with the situation where we can turn ->f_path into an anon union of const struct path f_path and struct path __f_path, the latter modified only in a few places in fs/{file_table,open,namei}.c, all for struct file instances that are yet to be opened" * tag 'pull-f_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (23 commits) Have cc(1) catch attempts to modify ->f_path kernel/acct.c: saner struct file treatment configfs:get_target() - release path as soon as we grab configfs_item reference apparmor/af_unix: constify struct path * arguments ovl_is_real_file: constify realpath argument ovl_sync_file(): constify path argument ovl_lower_dir(): constify path argument ovl_get_verity_digest(): constify path argument ovl_validate_verity(): constify {meta,data}path arguments ovl_ensure_verity_loaded(): constify datapath argument ksmbd_vfs_set_init_posix_acl(): constify path argument ksmbd_vfs_inherit_posix_acl(): constify path argument ksmbd_vfs_kern_path_unlock(): constify path argument ksmbd_vfs_path_lookup_locked(): root_share_path can be const struct path * check_export(): constify path argument export_operations->open(): constify path argument rqst_exp_get_by_name(): constify path argument nfs: constify path argument of __vfs_getattr() bpf...d_path(): constify path argument done_path_create(): constify path argument ...

nsfs: support file handles

2025-09-19T12:26:16+00:00

A while ago we added support for file handles to pidfs so pidfds can be encoded and decoded as file handles. Userspace has adopted this quickly and it's proven very useful. Implement file handles for namespaces as well. A process is not always able to open /proc/self/ns/. That requires procfs to be mounted and for /proc/self/ or /proc/self/ns/ to not be overmounted. However, userspace can always derive a namespace fd from a pidfd. And that always works for a task's own namespace. There's no need to introduce unnecessary behavioral differences between /proc/self/ns/ fds, pidfd-derived namespace fds, and file-handle-derived namespace fds. So namespace file handles are always decodable if the caller is located in the namespace the file handle refers to. This also allows a task to e.g., store a set of file handles to its namespaces in a file on-disk so it can verify when it gets rexeced that they're still valid and so on. This is akin to the pidfd use-case. Or just plainly for namespace comparison reasons where a file handle to the task's own namespace can be easily compared against others. Reviewed-by: Amir Goldstein Signed-off-by: Christian Brauner

export_operations->open(): constify path argument

2025-09-16T01:17:08+00:00

for the method and its sole instance... Reviewed-by: Jan Kara Reviewed-by: Christian Brauner Signed-off-by: Al Viro

docs/vfs: update references to i_mutex to i_rwsem

2025-06-23T10:17:33+00:00

VFS has switched to i_rwsem for ten years now (9902af79c01a: parallel lookups actual switch to rwsem), but the VFS documentation and comments still has references to i_mutex. Signed-off-by: Junxuan Liao Link: https://lore.kernel.org/72223729-5471-474a-af3c-f366691fba82@cs.wisc.edu Signed-off-by: Christian Brauner

exportfs: require ->fh_to_parent() to encode connectable file handles

2025-05-30T05:30:47+00:00

When user requests a connectable file handle explicitly with the AT_HANDLE_CONNECTABLE flag, fail the request if filesystem (e.g. nfs) does not know how to decode a connected non-dir dentry. Fixes: c374196b2b9f ("fs: name_to_handle_at() support for "explicit connectable" file handles") Signed-off-by: Amir Goldstein Link: https://lore.kernel.org/20250525104731.1461704-1-amir73il@gmail.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

nfsd: disallow file locking and delegations for NFSv4 reexport

2025-03-10T13:11:08+00:00

We do not and cannot support file locking with NFS reexport over NFSv4.x for the same reason we don't do it for NFSv3: NFS reexport server reboot cannot allow clients to recover locks because the source NFS server has not rebooted, and so it is not in grace. Since the source NFS server is not in grace, it cannot offer any guarantees that the file won't have been changed between the locks getting lost and any attempt to recover/reclaim them. The same applies to delegations and any associated locks, so disallow them too. Clients are no longer allowed to get file locks or delegations from a reexport server, any attempts will fail with operation not supported. Update the "Reboot recovery" section accordingly in Documentation/filesystems/nfs/reexport.rst Signed-off-by: Mike Snitzer Reviewed-by: Jeff Layton Signed-off-by: Chuck Lever

exportfs: add permission method

2024-12-17T08:16:11+00:00

This allows filesystems such as pidfs to provide their custom permission checks. Link: https://lore.kernel.org/r/20241129-work-pidfs-file_handle-v1-5-87d803a42495@kernel.org Reviewed-by: Amir Goldstein Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

exportfs: add open method

2024-12-14T11:40:41+00:00

This allows filesystems such as pidfs to provide their custom open. Link: https://lore.kernel.org/r/20241129-work-pidfs-file_handle-v1-3-87d803a42495@kernel.org Reviewed-by: Amir Goldstein Reviewed-by: Jan Kara Signed-off-by: Christian Brauner