kernel/linux.git/fs/fuse/passthrough.c, branch v7.0.10

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

fuse: move the backing file idr and code into a new source file

2025-09-25T14:06:02+00:00

iomap support for fuse is also going to want the ability to attach backing files to a fuse filesystem. Move the fuse_backing code into a separate file so that both can use it. Signed-off-by: Darrick J. Wong Reviewed-by: Amir Goldstein Signed-off-by: Miklos Szeredi

fuse: remove unused 'inode' parameter in fuse_passthrough_open

2025-08-27T12:29:44+00:00

The 'inode' parameter in fuse_passthrough_open() is never referenced in the function implementation. Signed-off-by: Chunsheng Luo Reviewed-by: Joanne Koong Signed-off-by: Miklos Szeredi

fuse: do not allow mapping a non-regular backing file

2025-08-26T10:43:31+00:00

We do not support passthrough operations other than read/write on regular file, so allowing non-regular backing files makes no sense. Fixes: efad7153bf93 ("fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN") Cc: stable@vger.kernel.org Signed-off-by: Amir Goldstein Reviewed-by: Bernd Schubert Signed-off-by: Miklos Szeredi

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

fuse: remove stray debug line

2024-10-25T15:05:49+00:00

It wasn't there when the patch was posted for review, but somehow made it into the pull. Link: https://lore.kernel.org/all/20240913104703.1673180-1-mszeredi@redhat.com/ Fixes: efad7153bf93 ("fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN") Signed-off-by: Miklos Szeredi

fuse: update inode size after extending passthrough write

2024-10-16T11:18:21+00:00

yangyun reported that libfuse test test_copy_file_range() copies zero bytes from a newly written file when fuse passthrough is enabled. The reason is that extending passthrough write is not updating the fuse inode size and when vfs_copy_file_range() observes a zero size inode, it returns without calling the filesystem copy_file_range() method. Fix this by adjusting the fuse inode size after an extending passthrough write. This does not provide cache coherency of fuse inode attributes and backing inode attributes, but it should prevent situations where fuse inode size is too small, causing read/copy to be wrongly shortened. Reported-by: yangyun Closes: https://github.com/libfuse/libfuse/issues/1048 Fixes: 57e1176e6086 ("fuse: implement read/write passthrough") Signed-off-by: Amir Goldstein Signed-off-by: Miklos Szeredi

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

fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN

2024-09-19T07:37:13+00:00

Only f_path is used from backing files registered with FUSE_DEV_IOC_BACKING_OPEN, so it makes sense to allow O_PATH descriptors. O_PATH files have an empty f_op, so don't check read_iter/write_iter. Reviewed-by: Amir Goldstein Signed-off-by: Miklos Szeredi

fuse: verify zero padding in fuse_backing_map

2024-04-22T15:13:43+00:00

To allow us extending the interface in the future. Fixes: 44350256ab94 ("fuse: implement ioctls to manage backing files") Signed-off-by: Amir Goldstein Signed-off-by: Miklos Szeredi