[PATCH v2] once: Fix panic when module unload

From: Kefeng Wang
Date: Fri Aug 06 2021 - 04:17:59 EST


DO_ONCE
DEFINE_STATIC_KEY_TRUE(___once_key);
__do_once_done
once_disable_jump(once_key);
INIT_WORK(&w->work, once_deferred);
struct once_work *w;
w->key = key;
schedule_work(&w->work); module unload
//*the key is
destroy*
process_one_work
once_deferred
BUG_ON(!static_key_enabled(work->key));
static_key_count((struct static_key *)x) //*access key, crash*

When module uses DO_ONCE mechanism, it could crash due to the above
concurrency problem, we could reproduce it with link[1].

Fix it by add/put module refcount in the once work process.

[1] https://lore.kernel.org/netdev/eaa6c371-465e-57eb-6be9-f4b16b9d7cbf@xxxxxxxxxx/

Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Minmin chen <chenmingmin@xxxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
v2: always pass THIS_MODULE to macro DO_ONCE(), suggested by hannes

include/linux/once.h | 4 ++--
lib/once.c | 11 ++++++++---
2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/once.h b/include/linux/once.h
index 9225ee6d96c7..ae6f4eb41cbe 100644
--- a/include/linux/once.h
+++ b/include/linux/once.h
@@ -7,7 +7,7 @@

bool __do_once_start(bool *done, unsigned long *flags);
void __do_once_done(bool *done, struct static_key_true *once_key,
- unsigned long *flags);
+ unsigned long *flags, struct module *mod);

/* Call a function exactly once. The idea of DO_ONCE() is to perform
* a function call such as initialization of random seeds, etc, only
@@ -46,7 +46,7 @@ void __do_once_done(bool *done, struct static_key_true *once_key,
if (unlikely(___ret)) { \
func(__VA_ARGS__); \
__do_once_done(&___done, &___once_key, \
- &___flags); \
+ &___flags, THIS_MODULE); \
} \
} \
___ret; \
diff --git a/lib/once.c b/lib/once.c
index 8b7d6235217e..59149bf3bfb4 100644
--- a/lib/once.c
+++ b/lib/once.c
@@ -3,10 +3,12 @@
#include <linux/spinlock.h>
#include <linux/once.h>
#include <linux/random.h>
+#include <linux/module.h>

struct once_work {
struct work_struct work;
struct static_key_true *key;
+ struct module *module;
};

static void once_deferred(struct work_struct *w)
@@ -16,10 +18,11 @@ static void once_deferred(struct work_struct *w)
work = container_of(w, struct once_work, work);
BUG_ON(!static_key_enabled(work->key));
static_branch_disable(work->key);
+ module_put(work->module);
kfree(work);
}

-static void once_disable_jump(struct static_key_true *key)
+static void once_disable_jump(struct static_key_true *key, struct module *mod)
{
struct once_work *w;

@@ -29,6 +32,8 @@ static void once_disable_jump(struct static_key_true *key)

INIT_WORK(&w->work, once_deferred);
w->key = key;
+ w->module = mod;
+ __module_get(mod);
schedule_work(&w->work);
}

@@ -53,11 +58,11 @@ bool __do_once_start(bool *done, unsigned long *flags)
EXPORT_SYMBOL(__do_once_start);

void __do_once_done(bool *done, struct static_key_true *once_key,
- unsigned long *flags)
+ unsigned long *flags, struct module *mod)
__releases(once_lock)
{
*done = true;
spin_unlock_irqrestore(&once_lock, *flags);
- once_disable_jump(once_key);
+ once_disable_jump(once_key, mod);
}
EXPORT_SYMBOL(__do_once_done);
--
2.26.2