Re: [PATCH v2 1/2] liveupdate: prevent double management of files

[Mike Rapoport <rppt@kernel.org>]

On Mon, Mar 23, 2026 at 08:31:44PM +0000, Pasha Tatashin wrote:
> Currently, LUO does not prevent the same file from being managed twice
> across different active sessions.
> 
> Use a global xarray `luo_preserved_files_xa` to keep track of file

Do we really need _xa suffix?

> pointers being preserved by LUO. Update luo_preserve_file() to check and
> insert the file pointer into this xarray when it is preserved, and
> erase it in luo_file_unpreserve_files() when it is released.
> 
> This ensures that the same file (struct file) cannot be managed by
> multiple sessions. If another session attempts to preserve an already
> managed file, it will now fail with -EBUSY.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
>  kernel/liveupdate/luo_file.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> index a38ea4975824..5f48c3c8c561 100644
> --- a/kernel/liveupdate/luo_file.c
> +++ b/kernel/liveupdate/luo_file.c
> @@ -110,11 +110,15 @@
>  #include <linux/sizes.h>
>  #include <linux/slab.h>
>  #include <linux/string.h>
> +#include <linux/xarray.h>
>  #include "luo_internal.h"
>  
>  static DECLARE_RWSEM(luo_file_handler_lock);
>  static LIST_HEAD(luo_file_handler_list);
>  
> +/* Keep track of files being preserved by LUO */
> +static DEFINE_XARRAY(luo_preserved_files_xa);
> +
>  /* 2 4K pages, give space for 128 files per file_set */
>  #define LUO_FILE_PGCNT		2ul
>  #define LUO_FILE_MAX							\
> @@ -249,6 +253,7 @@ static bool luo_token_is_used(struct luo_file_set *file_set, u64 token)
>   * Context: Can be called from an ioctl handler during normal system operation.
>   * Return: 0 on success. Returns a negative errno on failure:
>   *         -EEXIST if the token is already used.
> + *         -EBUSY if the file descriptor is already preserved by another session.
>   *         -EBADF if the file descriptor is invalid.
>   *         -ENOSPC if the file_set is full.
>   *         -ENOENT if no compatible handler is found.
> @@ -277,6 +282,11 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
>  	if (err)
>  		goto  err_fput;
>  
> +	err = xa_insert(&luo_preserved_files_xa, (unsigned long)file,
> +			file, GFP_KERNEL);
> +	if (err)
> +		goto err_free_files_mem;
> +
>  	err = -ENOENT;
>  	scoped_guard(rwsem_read, &luo_file_handler_lock) {
>  		list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> @@ -289,11 +299,11 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
>  
>  	/* err is still -ENOENT if no handler was found */
>  	if (err)
> -		goto err_free_files_mem;
> +		goto err_erase_xa;
>  
>  	err = luo_flb_file_preserve(fh);
>  	if (err)
> -		goto err_free_files_mem;
> +		goto err_erase_xa;
>  
>  	luo_file = kzalloc_obj(*luo_file);
>  	if (!luo_file) {
> @@ -323,6 +333,8 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
>  	kfree(luo_file);
>  err_flb_unpreserve:
>  	luo_flb_file_unpreserve(fh);
> +err_erase_xa:
> +	xa_erase(&luo_preserved_files_xa, (unsigned long)file);
>  err_free_files_mem:
>  	luo_free_files_mem(file_set);
>  err_fput:
> @@ -366,6 +378,7 @@ void luo_file_unpreserve_files(struct luo_file_set *file_set)
>  		luo_file->fh->ops->unpreserve(&args);
>  		luo_flb_file_unpreserve(luo_file->fh);
>  
> +		xa_erase(&luo_preserved_files_xa, (unsigned long)luo_file->file);
>  		list_del(&luo_file->list);
>  		file_set->count--;
>  
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.