Change liveupdate_unregister_file_handler and liveupdate_unregister_flb
to return void instead of an error code. This follows the design
principle that unregistration during module unload should not fail,
as the unload cannot be stopped at that point.
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
include/linux/liveupdate.h | 14 ++++++--------
kernel/liveupdate/luo_file.c | 14 ++------------
kernel/liveupdate/luo_flb.c | 11 +++--------
3 files changed, 11 insertions(+), 28 deletions(-)
diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
index 73ca84de3eae..2ae27711ac41 100644
--- a/include/linux/liveupdate.h
+++ b/include/linux/liveupdate.h
@@ -229,12 +229,12 @@ bool liveupdate_enabled(void);
int liveupdate_reboot(void);
int liveupdate_register_file_handler(struct liveupdate_file_handler *fh);
-int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh);
+void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh);
int liveupdate_register_flb(struct liveupdate_file_handler *fh,
struct liveupdate_flb *flb);
-int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
- struct liveupdate_flb *flb);
+void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
+ struct liveupdate_flb *flb);
int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp);
int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp);
@@ -256,9 +256,8 @@ static inline int liveupdate_register_file_handler(struct liveupdate_file_handle
return -EOPNOTSUPP;
}
-static inline int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
+static inline void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
{
- return -EOPNOTSUPP;
}
static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh,
@@ -267,10 +266,9 @@ static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh,
return -EOPNOTSUPP;
}
-static inline int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
- struct liveupdate_flb *flb)
+static inline void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
+ struct liveupdate_flb *flb)
{
- return -EOPNOTSUPP;
}
static inline int liveupdate_flb_get_incoming(struct liveupdate_flb *flb,
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index dd55e5e74d69..761e8f7cfc82 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -884,25 +884,15 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
*
* Unregisters the file handler from the liveupdate core. This function
* reverses the operations of liveupdate_register_file_handler().
- *
- * It ensures safe removal by checking that:
- * No FLB registered with this file handler.
- *
- * If the unregistration fails, the internal test state is reverted.
- *
- * Return: 0 Success. -EOPNOTSUPP when live update is not enabled. -EBUSY A live
- * update is in progress, FLB is registred with this file handler.
*/
-int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
+void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
{
if (!liveupdate_enabled())
- return -EOPNOTSUPP;
+ return;
guard(rwsem_write)(&luo_register_rwlock);
luo_flb_unregister_all(fh);
list_del(&ACCESS_PRIVATE(fh, list));
module_put(fh->ops->owner);
-
- return 0;
}
diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index f8348138de70..8f3c9c63e320 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -492,21 +492,16 @@ int liveupdate_register_flb(struct liveupdate_file_handler *fh,
* owner module (acquired during registration) is released.
*
* Context: It is typically called from a subsystem's module exit function.
- * Return: 0 on success.
- * -EOPNOTSUPP if live update is disabled.
- * -ENOENT if the FLB was not found in the file handler's list.
*/
-int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
- struct liveupdate_flb *flb)
+void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
+ struct liveupdate_flb *flb)
{
if (!liveupdate_enabled())
- return -EOPNOTSUPP;
+ return;
guard(rwsem_write)(&luo_register_rwlock);
luo_flb_unregister_one(fh, flb);
-
- return 0;
}
/**
--
2.43.0On Thu, Mar 26, 2026 at 11:33 PM Pasha Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> Change liveupdate_unregister_file_handler and liveupdate_unregister_flb
> to return void instead of an error code. This follows the design
> principle that unregistration during module unload should not fail,
> as the unload cannot be stopped at that point.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/linux/liveupdate.h | 14 ++++++--------
> kernel/liveupdate/luo_file.c | 14 ++------------
> kernel/liveupdate/luo_flb.c | 11 +++--------
> 3 files changed, 11 insertions(+), 28 deletions(-)
>
> diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
> index 73ca84de3eae..2ae27711ac41 100644
> --- a/include/linux/liveupdate.h
> +++ b/include/linux/liveupdate.h
> @@ -229,12 +229,12 @@ bool liveupdate_enabled(void);
> int liveupdate_reboot(void);
>
> int liveupdate_register_file_handler(struct liveupdate_file_handler *fh);
> -int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh);
> +void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh);
>
> int liveupdate_register_flb(struct liveupdate_file_handler *fh,
> struct liveupdate_flb *flb);
> -int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
> - struct liveupdate_flb *flb);
> +void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
> + struct liveupdate_flb *flb);
>
> int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp);
> int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp);
> @@ -256,9 +256,8 @@ static inline int liveupdate_register_file_handler(struct liveupdate_file_handle
> return -EOPNOTSUPP;
> }
>
> -static inline int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
> +static inline void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
> {
> - return -EOPNOTSUPP;
> }
>
> static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh,
> @@ -267,10 +266,9 @@ static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh,
> return -EOPNOTSUPP;
> }
>
> -static inline int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
> - struct liveupdate_flb *flb)
> +static inline void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
> + struct liveupdate_flb *flb)
> {
> - return -EOPNOTSUPP;
> }
>
> static inline int liveupdate_flb_get_incoming(struct liveupdate_flb *flb,
> diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> index dd55e5e74d69..761e8f7cfc82 100644
> --- a/kernel/liveupdate/luo_file.c
> +++ b/kernel/liveupdate/luo_file.c
> @@ -884,25 +884,15 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
> *
> * Unregisters the file handler from the liveupdate core. This function
> * reverses the operations of liveupdate_register_file_handler().
> - *
> - * It ensures safe removal by checking that:
> - * No FLB registered with this file handler.
> - *
> - * If the unregistration fails, the internal test state is reverted.
> - *
> - * Return: 0 Success. -EOPNOTSUPP when live update is not enabled. -EBUSY A live
> - * update is in progress, FLB is registred with this file handler.
> */
> -int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
> +void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
> {
> if (!liveupdate_enabled())
> - return -EOPNOTSUPP;
> + return;
>
> guard(rwsem_write)(&luo_register_rwlock);
> luo_flb_unregister_all(fh);
> list_del(&ACCESS_PRIVATE(fh, list));
>
> module_put(fh->ops->owner);
> -
> - return 0;
> }
> diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
> index f8348138de70..8f3c9c63e320 100644
> --- a/kernel/liveupdate/luo_flb.c
> +++ b/kernel/liveupdate/luo_flb.c
> @@ -492,21 +492,16 @@ int liveupdate_register_flb(struct liveupdate_file_handler *fh,
> * owner module (acquired during registration) is released.
> *
> * Context: It is typically called from a subsystem's module exit function.
> - * Return: 0 on success.
> - * -EOPNOTSUPP if live update is disabled.
> - * -ENOENT if the FLB was not found in the file handler's list.
> */
> -int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
> - struct liveupdate_flb *flb)
> +void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
> + struct liveupdate_flb *flb)
> {
> if (!liveupdate_enabled())
> - return -EOPNOTSUPP;
> + return;
>
> guard(rwsem_write)(&luo_register_rwlock);
>
> luo_flb_unregister_one(fh, flb);
> -
> - return 0;
> }
A question from Sashiko:
If the file handler is unregistered and freed by its owner, its dependent
FLBs might still retain a stale pointer to it. When an FLB is later
unregistered and calls liveupdate_unregister_flb() with this stale fh
pointer, could luo_flb_unregister_one() dereference the freed memory and
cause a use-after-free?
No, there is no UAF possability here.
1. FLBs do not keep pointers to file handlers.
The relationship between file handlers and FLBs is asymmetric. A
struct liveupdate_file_handler maintains a list of its dependent FLBs
in its flb_list. And, the struct liveupdate_flb only tracks the number
of handlers using it and its position in a global list. It does not
store pointers back to the file handlers.
2. Manual FLB unregistration: When a subsystem calls
liveupdate_unregister_flb, it is responsible for providing a valid fh
pointer. Since the subsystem typically owns the lifetime of the fh (a
static structure in the module), it is the caller's responsibility not
to pass a stale pointer.
3. Atomatic FLB unregistration during
liveupdate_unregister_file_handler function, explicitly calls
luo_flb_unregister_all(fh): luo_flb_unregister_all(fh) iterates
through the handler's flb_list, calls luo_flb_unregister_one for each,
which removes the luo_flb_link from the handler and frees it. This
ensures that when the handler is gone, all its associations with FLBs
are already destroyed.
Pasha
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