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[188.32.236.56]) by smtp.gmail.com with ESMTPSA id f21sm548520lfe.6.2021.01.21.06.30.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Jan 2021 06:30:42 -0800 (PST) Reply-To: efremov@linux.com To: Gaurav Kohli , rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, stable@vger.kernel.org References: <1601976833-24377-1-git-send-email-gkohli@codeaurora.org> From: Denis Efremov Subject: Re: [PATCH v1] trace: Fix race in trace_open and buffer resize call Message-ID: Date: Thu, 21 Jan 2021 17:30:40 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <1601976833-24377-1-git-send-email-gkohli@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org Hi, This patch (CVE-2020-27825) was tagged with Fixes: b23d7a5f4a07a ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU") I'm not an expert here but it seems like b23d7a5f4a07a only refactored ring_buffer_reset_cpu() by introducing reset_disabled_cpu_buffer() without significant changes. Hence, mutex_lock(&buffer->mutex)/mutex_unlock(&buffer->mutex) can be backported further than b23d7a5f4a07a~ and to all LTS kernels. Is b23d7a5f4a07a the actual cause of the bug? Thanks, Denis On 10/6/20 12:33 PM, Gaurav Kohli wrote: > Below race can come, if trace_open and resize of > cpu buffer is running parallely on different cpus > CPUX CPUY > ring_buffer_resize > atomic_read(&buffer->resize_disabled) > tracing_open > tracing_reset_online_cpus > ring_buffer_reset_cpu > rb_reset_cpu > rb_update_pages > remove/insert pages > resetting pointer > > This race can cause data abort or some times infinte loop in > rb_remove_pages and rb_insert_pages while checking pages > for sanity. > > Take buffer lock to fix this. > > Signed-off-by: Gaurav Kohli > Cc: stable@vger.kernel.org > --- > Changes since v0: > -Addressed Steven's review comments. > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 93ef0ab..15bf28b 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -4866,6 +4866,9 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu) > if (!cpumask_test_cpu(cpu, buffer->cpumask)) > return; > > + /* prevent another thread from changing buffer sizes */ > + mutex_lock(&buffer->mutex); > + > atomic_inc(&cpu_buffer->resize_disabled); > atomic_inc(&cpu_buffer->record_disabled); > > @@ -4876,6 +4879,8 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu) > > atomic_dec(&cpu_buffer->record_disabled); > atomic_dec(&cpu_buffer->resize_disabled); > + > + mutex_unlock(&buffer->mutex); > } > EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu); > > @@ -4889,6 +4894,9 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer) > struct ring_buffer_per_cpu *cpu_buffer; > int cpu; > > + /* prevent another thread from changing buffer sizes */ > + mutex_lock(&buffer->mutex); > + > for_each_online_buffer_cpu(buffer, cpu) { > cpu_buffer = buffer->buffers[cpu]; > > @@ -4907,6 +4915,8 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer) > atomic_dec(&cpu_buffer->record_disabled); > atomic_dec(&cpu_buffer->resize_disabled); > } > + > + mutex_unlock(&buffer->mutex); > } > > /** >