From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: + kmod-make-request_module-return-an-error-when-autoloading-is-disabled.patch added to -mm tree Date: Tue, 10 Mar 2020 16:59:49 -0700 Message-ID: <20200310235949.Ms2NVumcd%akpm@linux-foundation.org> References: <20200305222751.6d781a3f2802d79510941e4e@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:60542 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726899AbgCJX7v (ORCPT ); Tue, 10 Mar 2020 19:59:51 -0400 In-Reply-To: <20200305222751.6d781a3f2802d79510941e4e@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: ast@kernel.org, ebiggers@google.com, gregkh@linuxfoundation.org, jeffv@google.com, jeyu@kernel.org, keescook@chromium.org, mcgrof@kernel.org, mm-commits@vger.kernel.org, stable@vger.kernel.org The patch titled Subject: kmod: make request_module() return an error when autoloading is disabled has been added to the -mm tree. Its filename is kmod-make-request_module-return-an-error-when-autoloading-is-disabled.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/kmod-make-request_module-return-an-error-when-autoloading-is-disabled.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/kmod-make-request_module-return-an-error-when-autoloading-is-disabled.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Eric Biggers Subject: kmod: make request_module() return an error when autoloading is disabled It's long been possible to disable kernel module autoloading completely by setting /proc/sys/kernel/modprobe to the empty string. This can be preferable to setting it to a nonexistent file since it avoids the overhead of an attempted execve(), avoids potential deadlocks, and avoids the call to security_kernel_module_request() and thus on SELinux-based systems eliminates the need to write SELinux rules to dontaudit module_request. However, when module autoloading is disabled in this way, request_module() returns 0. This is broken because callers expect 0 to mean that the module was successfully loaded. Apparently this was never noticed because this method of disabling module autoloading isn't used much, and also most callers don't use the return value of request_module() since it's always necessary to check whether the module registered its functionality or not anyway. But improperly returning 0 can indeed confuse a few callers, for example get_fs_type() in fs/filesystems.c where it causes a WARNING to be hit: if (!fs && (request_module("fs-%.*s", len, name) == 0)) { fs = __get_fs_type(name, len); WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs? ", len, name); } This is easily reproduced with: echo > /proc/sys/kernel/modprobe mount -t NONEXISTENT none / It causes: request_module fs-NONEXISTENT succeeded, but still no fs? WARNING: CPU: 1 PID: 1106 at fs/filesystems.c:275 get_fs_type+0xd6/0xf0 [...] Arguably this warning is broken and should be removed, since the module could have been unloaded already. However, request_module() should also correctly return an error when it fails. So let's make it return -ENOENT, which matches the error when the modprobe binary doesn't exist. Link: http://lkml.kernel.org/r/20200310223731.126894-1-ebiggers@kernel.org Signed-off-by: Eric Biggers Cc: Alexei Starovoitov Cc: Greg Kroah-Hartman Cc: Jeff Vander Stoep Cc: Jessica Yu Cc: Kees Cook Cc: Luis Chamberlain Cc: Signed-off-by: Andrew Morton --- kernel/kmod.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/kernel/kmod.c~kmod-make-request_module-return-an-error-when-autoloading-is-disabled +++ a/kernel/kmod.c @@ -120,7 +120,7 @@ out: * invoke it. * * If module auto-loading support is disabled then this function - * becomes a no-operation. + * simply returns -ENOENT. */ int __request_module(bool wait, const char *fmt, ...) { @@ -137,7 +137,7 @@ int __request_module(bool wait, const ch WARN_ON_ONCE(wait && current_is_async()); if (!modprobe_path[0]) - return 0; + return -ENOENT; va_start(args, fmt); ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args); _ Patches currently in -mm which might be from ebiggers@google.com are kmod-make-request_module-return-an-error-when-autoloading-is-disabled.patch