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

[Samiullah Khawaja <skhawaja@google.com>]

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
>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
>

Reviewed-by: Samiullah Khawaja <skhawaja@google.com>