From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752384AbdHIXqo (ORCPT ); Wed, 9 Aug 2017 19:46:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:40874 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752022AbdHIXqn (ORCPT ); Wed, 9 Aug 2017 19:46:43 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DF0D022C93 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=mcgrof@kernel.org From: "Luis R. Rodriguez" To: akpm@linux-foundation.org Cc: mingo@redhat.com, peterz@infradead.org, keescook@chromium.org, dmitry.torokhov@gmail.com, jeyu@redhat.com, rusty@rustcorp.com.au, mmarek@suse.com, pmladek@suse.com, mbenes@suse.cz, jpoimboe@redhat.com, ebiederm@xmission.com, shuah@kernel.org, matt.redfearn@imgtec.com, dan.carpenter@oracle.com, colin.king@canonical.com, danielmentz@google.com, dcb314@hotmail.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, "Luis R. Rodriguez" Subject: [PATCH 2/3] kmod: fix wait on recursive loop Date: Wed, 9 Aug 2017 16:46:34 -0700 Message-Id: <20170809234635.13443-3-mcgrof@kernel.org> X-Mailer: git-send-email 2.13.2 In-Reply-To: <20170809234635.13443-1-mcgrof@kernel.org> References: <20170809234635.13443-1-mcgrof@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Recursive loops with module loading were previously handled in kmod by restricting the number of modprobe calls to 50 and if that limit was breached request_module() would return an error and a user would see the following on their kernel dmesg: request_module: runaway loop modprobe binfmt-464c Starting init:/sbin/init exists but couldn't execute it (error -8) This issue could happen for instance when a 64-bit kernel boots a 32-bit userspace on some architectures and has no 32-bit binary format hanlders. This is visible, for instance, when a CONFIG_MODULES enabled 64-bit MIPS kernel boots a into o32 root filesystem and the binfmt handler for o32 binaries is not built-in. After commit 6d7964a722af ("kmod: throttle kmod thread limit") we now don't have any visible signs of an error and the kernel just waits for the loop to end somehow. Although this *particular* recursive loop could also be addressed by doing a sanity check on search_binary_handler() and disallowing a modular binfmt to be required for modprobe, a generic solution for any recursive kernel kmod issues is still needed. This should catch these loops. We can investigate each loop and address each one separately as they come in, this however puts a stop gap for them as before. Fixes: 6d7964a722af ("kmod: throttle kmod thread limit") Reported-by: Matt Redfearn Tested-by: Matt Redfearn Signed-off-by: Luis R. Rodriguez --- kernel/kmod.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/kernel/kmod.c b/kernel/kmod.c index 6d016c5d97c8..2f37acde640b 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -70,6 +70,18 @@ static DECLARE_RWSEM(umhelper_sem); static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT); static DECLARE_WAIT_QUEUE_HEAD(kmod_wq); +/* + * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads + * running at the same time without returning. When this happens we + * believe you've somehow ended up with a recursive module dependency + * creating a loop. + * + * We have no option but to fail. + * + * Userspace should proactively try to detect and prevent these. + */ +#define MAX_KMOD_ALL_BUSY_TIMEOUT 5 + /* modprobe_path is set via /proc/sys. */ @@ -167,8 +179,17 @@ int __request_module(bool wait, const char *fmt, ...) pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...", atomic_read(&kmod_concurrent_max), MAX_KMOD_CONCURRENT, module_name); - wait_event_interruptible(kmod_wq, - atomic_dec_if_positive(&kmod_concurrent_max) >= 0); + ret = wait_event_killable_timeout(kmod_wq, + atomic_dec_if_positive(&kmod_concurrent_max) >= 0, + MAX_KMOD_ALL_BUSY_TIMEOUT * HZ); + if (!ret) { + pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now", + module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT); + return -ETIME; + } else if (ret == -ERESTARTSYS) { + pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name); + return ret; + } } trace_module_request(module_name, wait, _RET_IP_); -- 2.14.0