From patchwork Tue Apr 21 07:05:03 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tiezhu Yang X-Patchwork-Id: 11500579 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 101ED81 for ; Tue, 21 Apr 2020 07:05:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 006032087E for ; Tue, 21 Apr 2020 07:05:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726626AbgDUHFR (ORCPT ); Tue, 21 Apr 2020 03:05:17 -0400 Received: from mail.loongson.cn ([114.242.206.163]:41452 "EHLO loongson.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726388AbgDUHFR (ORCPT ); Tue, 21 Apr 2020 03:05:17 -0400 Received: from linux.localdomain (unknown [113.200.148.30]) by mail.loongson.cn (Coremail) with SMTP id AQAAf9Dxf2ogm55esnIqAA--.25S5; Tue, 21 Apr 2020 15:05:07 +0800 (CST) From: Tiezhu Yang To: Luis Chamberlain , Shuah Khan , Andrew Morton , Jessica Yu Cc: linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Markus Elfring , Xuefeng Li Subject: [PATCH v4 3/4] kmod: Return directly if module name is empty in request_module() Date: Tue, 21 Apr 2020 15:05:03 +0800 Message-Id: <1587452704-1299-4-git-send-email-yangtiezhu@loongson.cn> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1587452704-1299-1-git-send-email-yangtiezhu@loongson.cn> References: <1587452704-1299-1-git-send-email-yangtiezhu@loongson.cn> X-CM-TRANSID: AQAAf9Dxf2ogm55esnIqAA--.25S5 X-Coremail-Antispam: 1UD129KBjvJXoWxZF4xAr13JF18CrW7GF4kWFg_yoW5GF43pa y5AFZ5Krs3t3yjya1xJrs7GryrK3y7JrW3Jr1DCrn3ZFZ0grnrAr1j9w15WFW8ua95Kw1U GF4vqw4fWF4Dur7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUBq14x267AKxVWrJVCq3wAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2048vs2IY020E87I2jVAFwI0_JrWl82xGYIkIc2 x26xkF7I0E14v26ryj6s0DM28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48ve4kI8wA2z4x0 Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI0_Cr0_Gr1UM2 8EF7xvwVC2z280aVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_GcCE3s1l e2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E2Ix0cI 8IcVAFwI0_Jrv_JF1lYx0Ex4A2jsIE14v26r4j6F4UMcvjeVCFs4IE7xkEbVWUJVW8JwAC jcxG0xvY0x0EwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lc2xSY4AK67AK6r4xMxAIw2 8IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr4l x2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y0x0EwIxGrw CI42IY6xIIjxv20xvE14v26r1I6r4UMIIF0xvE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwCI 42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z2 80aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7VUjNBMtUUUUU== X-CM-SenderInfo: p1dqw3xlh2x3gn0dqz5rrqw2lrqou0/ Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org If module name is empty, it is better to return directly at the beginning of request_module() without doing the needless call_modprobe() operation. (1) In the kernel space Call trace: request_module() | | __request_module() | | call_modprobe() | | call_usermodehelper_exec() -- retval = sub_info->retval; | | call_usermodehelper_exec_work() | | call_usermodehelper_exec_sync() -- sub_info->retval = ret; | | --> call_usermodehelper_exec_async() --> do_execve() | kernel_wait4(pid, (int __user *)&ret, 0, NULL); The exit status of child process is wrote to the address of variable "ret" after call kernel_wait4(), its value is 256 if module name is empty, then sub_info->retval is assigned to "ret" which is 256, the function call_usermodehelper_exec() returns 256, call_modprobe() and __request_module() also return 256. (2)In the user space when build and execute the following application, we can see the exit status is 256. $ ./system exit status = 256 $ ./execl exit status = 256 $ cat system.c #include #include int main() { int status = 0; status = system("modprobe '' > /dev/null 2>&1"); printf("exit status = %d\n", status); return status; } $ cat execl.c #include #include #include #include int main() { pid_t pid, w; int status; pid = fork(); if (pid == -1) { perror("fork"); exit(EXIT_FAILURE); } if (pid == 0) { execl("/bin/sh", "sh", "-c", "modprobe '' > /dev/null 2>&1", (char *) 0); } else { w = waitpid(pid, &status, 0); if (w == -1) { perror("waitpid"); exit(EXIT_FAILURE); } printf("exit status = %d\n", status); exit(EXIT_SUCCESS); } return 0; } The exit status of child process is wrote to the address of variable "status" after call waitpid() in the user space that corresponds with kernel_wait4() in the kernel space. Signed-off-by: Tiezhu Yang --- v4: - update the commit message with application v3: - no changes v2: - update the commit message to explain the detailed reason kernel/kmod.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/kmod.c b/kernel/kmod.c index 3cd075c..5851444 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -28,6 +28,8 @@ #include +#define MODULE_NOT_FOUND 256 + /* * Assuming: * @@ -144,6 +146,9 @@ int __request_module(bool wait, const char *fmt, ...) if (ret >= MODULE_NAME_LEN) return -ENAMETOOLONG; + if (strlen(module_name) == 0) + return MODULE_NOT_FOUND; + ret = security_kernel_module_request(module_name); if (ret) return ret;