From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) (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 D4C50125C0 for ; Fri, 29 Dec 2023 16:38:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=I-love.SAKURA.ne.jp Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=I-love.SAKURA.ne.jp Received: from fsav412.sakura.ne.jp (fsav412.sakura.ne.jp [133.242.250.111]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 3BTGb43q060179; Sat, 30 Dec 2023 01:37:04 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav412.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav412.sakura.ne.jp); Sat, 30 Dec 2023 01:37:04 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav412.sakura.ne.jp) Received: from [192.168.1.6] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 3BTGb4pS060174 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Sat, 30 Dec 2023 01:37:04 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <7227c8d1-08f6-4f95-ad0f-d5c3e47d874d@I-love.SAKURA.ne.jp> Date: Sat, 30 Dec 2023 01:37:04 +0900 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [kernel?] KMSAN: uninit-value in profile_hits (3) Content-Language: en-US To: syzbot , linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Hugh Dickins , Ingo Molnar References: <000000000000d6b55e060d6bc390@google.com> Cc: tglx@linutronix.de, paskripkin@gmail.com, rostedt@goodmis.org, glider@google.com, akpm@linux-foundation.org, ebiederm@xmission.com From: Tetsuo Handa In-Reply-To: <000000000000d6b55e060d6bc390@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit [PATCH] profiling: initialize prof_cpu_mask from profile_online_cpu() syzbot is reporting uninit-value at profile_hits(), for commit acd895795d35 ("profiling: fix broken profiling regression") by error initialized prof_cpu_mask too early. do_profile_hits() is called from profile_tick() from timer interrupt only if cpumask_test_cpu(smp_processor_id(), prof_cpu_mask) is true and prof_buffer is not NULL. But the syzbot's report says that profile_hits() was called while current thread is still doing vzalloc(buffer_bytes) where prof_buffer is NULL at this moment. This indicates two things. One is that cpumask_set_cpu(cpu, prof_cpu_mask) should have been called from profile_online_cpu() from cpuhp_setup_state() only after profile_init() completed. Fix this by explicitly calling cpumask_copy() from create_proc_profile() on only UP kernels. The other is that multiple threads concurrently tried to write to /sys/kernel/profiling interface, which caused that somebody else tried to re-initialize prof_buffer despite somebody has already initialized prof_buffer. Fix this by using serialization. Reported-by: syzbot+b1a83ab2a9eb9321fbdd@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=b1a83ab2a9eb9321fbdd Fixes: acd895795d35 ("profiling: fix broken profiling regression") Signed-off-by: Tetsuo Handa --- Please test before applying this patch; I don't know how to test this functionality. #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master kernel/ksysfs.c | 27 ++++++++++++++++++++++----- kernel/profile.c | 6 +++--- 2 files changed, 25 insertions(+), 8 deletions(-) diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c index 1d4bc493b2f4..66bc712f590c 100644 --- a/kernel/ksysfs.c +++ b/kernel/ksysfs.c @@ -91,10 +91,23 @@ static ssize_t profiling_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) { + static DEFINE_MUTEX(lock); int ret; - if (prof_on) - return -EEXIST; + /* + * We need serialization, for profile_setup() initializes prof_on + * value. Also, use killable wait in case memory allocation from + * profile_init() triggered the OOM killer and chose current thread + * blocked here. + */ + if (mutex_lock_killable(&lock)) + return -EINTR; + + if (prof_on) { + count = -EEXIST; + goto out; + } + /* * This eventually calls into get_option() which * has a ton of callers and is not const. It is @@ -102,11 +115,15 @@ static ssize_t profiling_store(struct kobject *kobj, */ profile_setup((char *)buf); ret = profile_init(); - if (ret) - return ret; + if (ret) { + count = ret; + goto out; + } ret = create_proc_profile(); if (ret) - return ret; + count = ret; +out: + mutex_unlock(&lock); return count; } KERNEL_ATTR_RW(profiling); diff --git a/kernel/profile.c b/kernel/profile.c index 8a77769bc4b4..7575747e2ac6 100644 --- a/kernel/profile.c +++ b/kernel/profile.c @@ -114,11 +114,9 @@ int __ref profile_init(void) buffer_bytes = prof_len*sizeof(atomic_t); - if (!alloc_cpumask_var(&prof_cpu_mask, GFP_KERNEL)) + if (!zalloc_cpumask_var(&prof_cpu_mask, GFP_KERNEL)) return -ENOMEM; - cpumask_copy(prof_cpu_mask, cpu_possible_mask); - prof_buffer = kzalloc(buffer_bytes, GFP_KERNEL|__GFP_NOWARN); if (prof_buffer) return 0; @@ -481,6 +479,8 @@ int __ref create_proc_profile(void) goto err_state_prep; online_state = err; err = 0; +#else + cpumask_copy(prof_cpu_mask, cpu_possible_mask); #endif entry = proc_create("profile", S_IWUSR | S_IRUGO, NULL, &profile_proc_ops); -- 2.18.4