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netdevsim: take bus device refcount before registering device

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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 <adrianox@gmail.com>
Link: https://patch.msgid.link/20260902025704.34606-1-adrianox@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Adriano Cordova 2026-09-01 22:57:04 -04:00 committed by Jakub Kicinski
parent a5249d1d9a
commit d5f5853f16
1 changed files with 4 additions and 3 deletions
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7
drivers/net/netdevsim/bus.c
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@ -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);