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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id w44sm21598195qtj.86.2020.08.11.11.42.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Aug 2020 11:42:49 -0700 (PDT) Subject: Re: [PATCH v3 1/5] btrfs: extent_io: Do extra check for extent buffer read write functions To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20200809120919.85271-1-wqu@suse.com> <20200809120919.85271-2-wqu@suse.com> From: Josef Bacik Message-ID: <26d258e9-4489-df31-d919-a672002863cc@toxicpanda.com> Date: Tue, 11 Aug 2020 14:42:48 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200809120919.85271-2-wqu@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 8/9/20 8:09 AM, Qu Wenruo wrote: > Although we have start, len check for extent buffer reader/write (e.g. > read_extent_buffer()), those checks has its limitations: > - No overflow check > Values like start = 1024 len = -1024 can still pass the basic > (start + len) > eb->len check. > > - Checks are not consistent > For read_extent_buffer() we only check (start + len) against eb->len. > While for memcmp_extent_buffer() we also check start against eb->len. > > - Different error reporting mechanism > We use WARN() in read_extent_buffer() but BUG() in > memcpy_extent_buffer(). > > - Still modify memory if the request is obviously wrong > In read_extent_buffer() even we find (start + len) > eb->len, we still > call memset(dst, 0, len), which can eaisly cause memory access error > if start + len overflows. > > To address above problems, this patch creates a new common function to > check such access, check_eb_range(). > - Add overflow check > This function checks start, start + len against eb->len and overflow > check. > > - Unified checks > > - Unified error reports > Will call WARN() if CONFIG_BTRFS_DEBUG is configured. > And also do btrfs_warn() message for non-debug build. > > - Exit ASAP if check fails > No more possible memory corruption. > > - Add extra comment for @start @len used in those functions > Even experienced developers sometimes get confused with the @start > @len with logical address in those functions. > I'm not sure what's the cause, maybe it's the extent_buffer::start > naming. > For now, just add some comment. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=202817 > [ Inspired by above report, the report itself is already addressed ] > Signed-off-by: Qu Wenruo Reviewed-by: Josef Bacik Thanks, Josef