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Miller" , Eric Dumazet , Paolo Abeni , linux-kernel@vger.kernel.org, Adriano Cordova , syzbot+989ff6506f5c6d1ff56b@syzkaller.appspot.com Subject: [PATCH net] netdevsim: take bus device refcount before registering device Date: Mon, 31 Aug 2026 14:39:52 -0400 Message-ID: <20260831183952.1345042-1-adrianox@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nsim_bus_dev_release() drops nsim_bus_devs when a device is freed, but the matching increment was done in new_device_store() only after nsim_bus_dev_new() returned successfully. When device_register() failed inside nsim_bus_dev_new(), put_device() invoked the release callback and decremented nsim_bus_devs without the increment, driving the refcount to zero. A later successful device creation then incremented from zero and triggered: refcount_t: addition on 0; use-after-free. Increment nsim_bus_devs in nsim_bus_dev_new() before device_register() so the release callback's decrement is balanced on both the success and error paths. Reported-by: syzbot+989ff6506f5c6d1ff56b@syzkaller.appspot.com Closes: https://syzkaller.appspot.com/bug?extid=989ff6506f5c6d1ff56b Fixes: 6aff7cbfe7bfa ("netdevsim: Block until all devices are released") Signed-off-by: Adriano Cordova --- drivers/net/netdevsim/bus.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c index 5c55c308487b..426fb438b922 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; -- 2.51.0