linux-stable.git/include/linux/backing-file.h, branch v7.0.4

lsm: add backing_file LSM hooks

2026-05-07T04:14:01+00:00

commit 6af36aeb147a06dea47c49859cd6ca5659aeb987 upstream.

Stacked filesystems such as overlayfs do not currently provide the
necessary mechanisms for LSMs to properly enforce access controls on the
mmap() and mprotect() operations.  In order to resolve this gap, a LSM
security blob is being added to the backing_file struct and the following
new LSM hooks are being created:

 security_backing_file_alloc()
 security_backing_file_free()
 security_mmap_backing_file()

The first two hooks are to manage the lifecycle of the LSM security blob
in the backing_file struct, while the third provides a new mmap() access
control point for the underlying backing file.  It is also expected that
LSMs will likely want to update their security_file_mprotect() callback
to address issues with their mprotect() controls, but that does not
require a change to the security_file_mprotect() LSM hook.

There are a three other small changes to support these new LSM hooks:
* Pass the user file associated with a backing file down to
alloc_empty_backing_file() so it can be included in the
security_backing_file_alloc() hook.
* Add getter and setter functions for the backing_file struct LSM blob
as the backing_file struct remains private to fs/file_table.c.
* Constify the file struct field in the LSM common_audit_data struct to
better support LSMs that need to pass a const file struct pointer into
the common LSM audit code.

Thanks to Arnd Bergmann for identifying the missing EXPORT_SYMBOL_GPL()
and supplying a fixup.

Cc: stable@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-unionfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Reviewed-by: Amir Goldstein 
Reviewed-by: Serge Hallyn 
Reviewed-by: Christian Brauner 
Signed-off-by: Paul Moore 
Signed-off-by: Greg Kroah-Hartman

backing-file: clean up the API

2024-11-11T09:45:03+00:00

 - Pass iocb to ctx->end_write() instead of file + pos

 - Get rid of ctx->user_file, which is redundant most of the time

 - Instead pass iocb to backing_file_splice_read and
   backing_file_splice_write

Signed-off-by: Miklos Szeredi 
Signed-off-by: Amir Goldstein

fs: pass offset and result to backing_file end_write() callback

2024-10-16T11:17:45+00:00

This is needed for extending fuse inode size after fuse passthrough write.

Suggested-by: Miklos Szeredi 
Link: https://lore.kernel.org/linux-fsdevel/CAJfpegs=cvZ_NYy6Q_D42XhYS=Sjj5poM1b5TzXzOVvX=R36aA@mail.gmail.com/
Signed-off-by: Amir Goldstein 
Signed-off-by: Miklos Szeredi

ovl: implement tmpfile

2024-05-02T18:35:57+00:00

Combine inode creation with opening a file.

There are six separate objects that are being set up: the backing inode,
dentry and file, and the overlay inode, dentry and file.  Cleanup in case
of an error is a bit of a challenge and is difficult to test, so careful
review is needed.

All tmpfile testcases except generic/509 now run/pass, and no regressions
are observed with full xfstests.

Signed-off-by: Miklos Szeredi 
Reviewed-by: Amir Goldstein

fs: factor out backing_file_mmap() helper

2023-12-23T14:35:09+00:00

Assert that the file object is allocated in a backing_file container
so that file_user_path() could be used to display the user path and
not the backing file's path in /proc//maps.

Signed-off-by: Amir Goldstein

fs: factor out backing_file_splice_{read,write}() helpers

2023-12-23T14:35:09+00:00

There is not much in those helpers, but it makes sense to have them
logically next to the backing_file_{read,write}_iter() helpers as they
may grow more common logic in the future.

Signed-off-by: Amir Goldstein

fs: factor out backing_file_{read,write}_iter() helpers

2023-12-23T14:35:09+00:00

Overlayfs submits files io to backing files on other filesystems.
Factor out some common helpers to perform io to backing files, into
fs/backing-file.c.

Suggested-by: Miklos Szeredi 
Link: https://lore.kernel.org/r/CAJfpeguhmZbjP3JLqtUy0AdWaHOkAPWeP827BBWwRFEAUgnUcQ@mail.gmail.com
Signed-off-by: Amir Goldstein

fs: prepare for stackable filesystems backing file helpers

2023-12-23T14:35:08+00:00

In preparation for factoring out some backing file io helpers from
overlayfs, move backing_file_open() into a new file fs/backing-file.c
and header.

Add a MAINTAINERS entry for stackable filesystems and add a Kconfig
FS_STACK which stackable filesystems need to select.

For now, the backing_file struct, the backing_file alloc/free functions
and the backing_file_real_path() accessor remain internal to file_table.c.
We may change that in the future.

Signed-off-by: Amir Goldstein