From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 57F2E455162; Mon, 31 Aug 2026 14:40:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788187244; cv=none; b=LZVILTvJFJDcYvGuaeiPggLA9J1Tjd57ouYBdLTvDQQLhw7YMYMpImqzUhr3fJwH7xvMNbuPxstcv6aOlRWAtGR2QrzThhK3aRKtnaROcOpRWupDau0tSTUeMyu975NSj+JjAZv/3JoYZnf/lRu3wC/BFaGLaF45SD98T31AFRM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788187244; c=relaxed/simple; bh=XnYbv/lvSUhA3IIkJg1wTTbKCIckEW6sc1YJvlWOlDc=; h=From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type:Date; b=jPtjbtRW6G7LoVUY/uZi+yQjnO+FSTX6/tPozdaTebYJ0glT+1egPqXFxbwi2ZpgXZjjKeEY9XqVAYxrKcECKIaonY5L5N2fJLnc34VqAcTpDEJ353VCXIMyIbL2LTGTUl+l0p0fWyWM0d51Y4wTKs8cjhBeaegTpvK6NW8517w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hfJBce/f; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hfJBce/f" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 769651F000E9; Mon, 31 Aug 2026 14:40:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788187243; bh=glU5brsq9stFhaeEUTYuaXur4gpoMrHcD9Sa+u8+sdg=; h=From:To:Cc:Subject:Date; b=hfJBce/fvMIR4mLQ4PXQ3TRh9fkfE4WBk2bYRVZ/iYYtplkxC3nwZMky4QTC5BLVI rPSzFKiGkQLoJ5WSVkzb9XC/I4n/OFEHTVNdKE8aaujzRwWgR154mDedpth9LTnhHv dizKdiUKcuNtNuqDIvaevQ7g94iF6667dQOy+kzY3qdiLiCSzWFfKJn8Mw3CVeiW6X lq7XAD0p/TzzLwGKcgVe4wmjr5Lcu5JPOpgmxAHTnjGKZhWTBKdjmsZQttCykmWI05 apiXUI8LXhjQoiOGeVnZLxQKusOXa2e1MRslSbEXjll5ShMj3AGMecd9ZwCDWn5jce jU0CQydiPoXMQ== From: "syzbot" To: syzkaller-bugs@googlegroups.com, "Wang, Jie" , "Chas Williams" <3chas3@gmail.com>, , "Greg Kroah-Hartman" , , , Cc: linux-kernel@vger.kernel.org, syzbot@lists.linux.dev Subject: [PATCH] usb: atm: cxacru: fix NULL pointer dereference on uninitialized atm_dev Message-ID: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Date: Mon, 31 Aug 2026 14:40:42 +0000 (UTC) From: "Wang, Jie" The cxacru driver uses the usbatm framework, which defers the ATM device registration to a kernel thread (usbatm_do_heavy_init()) but immediately returns success from the USB probe. Because the probe returns success, the driver core creates sysfs attribute files (like adsl_state and adsl_config), making them accessible to userspace before the ATM device is fully initialized. If a user writes to these sysfs files before the initialization is complete or if it fails, the driver attempts to send a command to the device. If the command fails, the error handling path calls atm_err(), which unconditionally dereferences instance->usbatm->atm_dev. Since atm_dev is NULL, this leads to a NULL pointer dereference: Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:adsl_state_store+0x5cc/0x770 drivers/usb/atm/cxacru.c:359 Call Trace: kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f To fix this, add checks for instance->usbatm->atm_dev == NULL in adsl_state_store() and adsl_config_store(). This prevents the functions from proceeding and dereferencing the uninitialized atm_dev, consistent with how mac_address_show() handles the same race condition. Fixes: e605c30977bb ("USB: atm: cxacru: convert to use dev_groups") Assisted-by: Gemini:gemini-3.6-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot+9b195c4f412ea5c4e56a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9b195c4f412ea5c4e56a Link: https://syzkaller.appspot.com/ai_job?id=b6352d63-d03a-4e87-92a4-b334c3ebcf97 Signed-off-by: "Wang, Jie" --- diff --git a/drivers/usb/atm/cxacru.c b/drivers/usb/atm/cxacru.c index 429ac20a8..dee15f7b7 100644 --- a/drivers/usb/atm/cxacru.c +++ b/drivers/usb/atm/cxacru.c @@ -347,7 +347,7 @@ static ssize_t adsl_state_store(struct device *dev, return -EINVAL; ret = 0; - if (instance == NULL) + if (instance == NULL || instance->usbatm->atm_dev == NULL) return -ENODEV; if (mutex_lock_interruptible(&instance->adsl_state_serialize)) @@ -444,7 +444,7 @@ static ssize_t adsl_config_store(struct device *dev, if (!capable(CAP_NET_ADMIN)) return -EACCES; - if (instance == NULL) + if (instance == NULL || instance->usbatm->atm_dev == NULL) return -ENODEV; pos = 0; base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. The person who has signed off on the patch is responsible for addressing comments. syzbot engineers can be reached at syzkaller@googlegroups.com.