From d5f5853f167fe2e584be013e111d03c1207969fe Mon Sep 17 00:00:00 2001 From: Adriano Cordova Date: Tue, 1 Sep 2026 22:57:04 -0400 Subject: [PATCH] netdevsim: take bus device refcount before registering device nsim_bus_dev_release() drops nsim_bus_devs when a device is freed, but the matching increment was done in new_device_store() after nsim_bus_dev_new() returned. When device_register() failed inside nsim_bus_dev_new(), put_device() invoked the release callback and decremented without an increment, driving the refcount to zero; a later creation then incremented from zero (refcount_t: addition on 0). Increment nsim_bus_devs in nsim_bus_dev_new() before device_register(), and drop the bus reference in nsim_bus_exit() only after every device has been removed, so the completion cannot be signaled early. Cc: stable+noautosel@kernel.org # netdevsim is a test harness, it's never loaded on production systems Reported-by: syzbot+989ff6506f5c6d1ff56b@syzkaller.appspot.com Closes: https://syzkaller.appspot.com/bug?extid=989ff6506f5c6d1ff56b Signed-off-by: Adriano Cordova Link: https://patch.msgid.link/20260902025704.34606-1-adrianox@gmail.com Signed-off-by: Jakub Kicinski --- drivers/net/netdevsim/bus.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c index 5c55c308487b..b792ee10b1c1 100644 --- a/drivers/net/netdevsim/bus.c +++ b/drivers/net/netdevsim/bus.c @@ -194,7 +194,6 @@ new_device_store(const struct bus_type *bus, const char *buf, size_t count) goto err; } - refcount_inc(&nsim_bus_devs); /* Allow using nsim_bus_dev */ smp_store_release(&nsim_bus_dev->init, true); @@ -465,6 +464,7 @@ nsim_bus_dev_new(unsigned int id, unsigned int port_count, unsigned int num_queu /* Disallow using nsim_bus_dev */ smp_store_release(&nsim_bus_dev->init, false); + refcount_inc(&nsim_bus_devs); err = device_register(&nsim_bus_dev->dev); if (err) goto err_nsim_bus_dev_id_free; @@ -520,8 +520,6 @@ void nsim_bus_exit(void) /* Disallow using resources */ smp_store_release(&nsim_bus_enable, false); - if (refcount_dec_and_test(&nsim_bus_devs)) - complete(&nsim_bus_devs_released); mutex_lock(&nsim_bus_dev_list_lock); list_for_each_entry_safe(nsim_bus_dev, tmp, &nsim_bus_dev_list, list) { @@ -530,6 +528,9 @@ void nsim_bus_exit(void) } mutex_unlock(&nsim_bus_dev_list_lock); + if (refcount_dec_and_test(&nsim_bus_devs)) + complete(&nsim_bus_devs_released); + wait_for_completion(&nsim_bus_devs_released); driver_unregister(&nsim_driver);