[PATCH 1/6] liveupdate: Protect file handler list with rwsem

Pasha Tatashin
2026-03-17T02:50:59Z

Because liveupdate file handlers will eventually no longer hold a
module reference when registered, we must ensure that the access to
the handler list is protected against concurrent module unloading.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
kernel/liveupdate/luo_file.c | 61 +++++++++++++++++++++---------------
1 file changed, 35 insertions(+), 26 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 5acee4174bf0..6a0ae29c6a24 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -112,6 +112,7 @@
#include <linux/string.h>
#include "luo_internal.h"

+static DECLARE_RWSEM(luo_file_handler_lock);
static LIST_HEAD(luo_file_handler_list);

/* 2 4K pages, give space for 128 files per file_set */
@@ -277,10 +278,12 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
goto err_fput;

err = -ENOENT;
- list_private_for_each_entry(fh, &luo_file_handler_list, list) {
- if (fh->ops->can_preserve(fh, file)) {
- err = 0;
- break;
+ scoped_guard(rwsem_read, &luo_file_handler_lock) {
+ list_private_for_each_entry(fh, &luo_file_handler_list, list) {
+ if (fh->ops->can_preserve(fh, file)) {
+ err = 0;
+ break;
+ }
}
}

@@ -777,10 +780,12 @@ int luo_file_deserialize(struct luo_file_set *file_set,
bool handler_found = false;
struct luo_file *luo_file;

- list_private_for_each_entry(fh, &luo_file_handler_list, list) {
- if (!strcmp(fh->compatible, file_ser[i].compatible)) {
- handler_found = true;
- break;
+ scoped_guard(rwsem_read, &luo_file_handler_lock) {
+ list_private_for_each_entry(fh, &luo_file_handler_list, list) {
+ if (!strcmp(fh->compatible, file_ser[i].compatible)) {
+ handler_found = true;
+ break;
+ }
}
}

@@ -850,25 +855,27 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
if (!luo_session_quiesce())
return -EBUSY;

- /* Check for duplicate compatible strings */
- list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
- if (!strcmp(fh_iter->compatible, fh->compatible)) {
- pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
- fh->compatible);
- err = -EEXIST;
+ scoped_guard(rwsem_write, &luo_file_handler_lock) {
+ /* Check for duplicate compatible strings */
+ list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
+ if (!strcmp(fh_iter->compatible, fh->compatible)) {
+ pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
+ fh->compatible);
+ err = -EEXIST;
+ goto err_resume;
+ }
+ }
+
+ /* Pin the module implementing the handler */
+ if (!try_module_get(fh->ops->owner)) {
+ err = -EAGAIN;
goto err_resume;
}
- }

- /* Pin the module implementing the handler */
- if (!try_module_get(fh->ops->owner)) {
- err = -EAGAIN;
- goto err_resume;
+ INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, flb_list));
+ INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, list));
+ list_add_tail(&ACCESS_PRIVATE(fh, list), &luo_file_handler_list);
}
-
- INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, flb_list));
- INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, list));
- list_add_tail(&ACCESS_PRIVATE(fh, list), &luo_file_handler_list);
luo_session_resume();

liveupdate_test_register(fh);
@@ -909,10 +916,12 @@ int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
if (!luo_session_quiesce())
goto err_register;

- if (!list_empty(&ACCESS_PRIVATE(fh, flb_list)))
- goto err_resume;
+ scoped_guard(rwsem_write, &luo_file_handler_lock) {
+ if (!list_empty(&ACCESS_PRIVATE(fh, flb_list)))
+ goto err_resume;

- list_del(&ACCESS_PRIVATE(fh, list));
+ list_del(&ACCESS_PRIVATE(fh, list));
+ }
module_put(fh->ops->owner);
luo_session_resume();

--
2.53.0.851.ga537e3e6e9-goog