From 6af36aeb147a06dea47c49859cd6ca5659aeb987 Mon Sep 17 00:00:00 2001 From: Paul Moore Date: Fri, 19 Dec 2025 13:18:22 -0500 Subject: lsm: add backing_file LSM hooks 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 --- include/linux/backing-file.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include/linux/backing-file.h') diff --git a/include/linux/backing-file.h b/include/linux/backing-file.h index 1476a6ed1bfd..c939cd222730 100644 --- a/include/linux/backing-file.h +++ b/include/linux/backing-file.h @@ -18,10 +18,10 @@ struct backing_file_ctx { void (*end_write)(struct kiocb *iocb, ssize_t); }; -struct file *backing_file_open(const struct path *user_path, int flags, +struct file *backing_file_open(const struct file *user_file, int flags, const struct path *real_path, const struct cred *cred); -struct file *backing_tmpfile_open(const struct path *user_path, int flags, +struct file *backing_tmpfile_open(const struct file *user_file, int flags, const struct path *real_parentpath, umode_t mode, const struct cred *cred); ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter, -- cgit v1.2.3