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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id l2sm3190445qtk.41.2021.11.12.06.29.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Nov 2021 06:29:25 -0800 (PST) Date: Fri, 12 Nov 2021 09:29:24 -0500 From: Josef Bacik To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org, Omar Sandoval Subject: Re: [PATCH v2] btrfs: fix a out-of-boundary access for copy_compressed_data_to_page() Message-ID: References: <20211112044730.25161-1-wqu@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211112044730.25161-1-wqu@suse.com> Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Nov 12, 2021 at 12:47:30PM +0800, Qu Wenruo wrote: > [BUG] > The following script can cause btrfs to crash: > > mount -o compress-force=lzo $DEV /mnt > dd if=/dev/urandom of=/mnt/foo bs=4k count=1 > sync > > The calltrace looks like this: > > general protection fault, probably for non-canonical address 0xe04b37fccce3b000: 0000 [#1] PREEMPT SMP NOPTI > CPU: 5 PID: 164 Comm: kworker/u20:3 Not tainted 5.15.0-rc7-custom+ #4 > Workqueue: btrfs-delalloc btrfs_work_helper [btrfs] > RIP: 0010:__memcpy+0x12/0x20 > Call Trace: > lzo_compress_pages+0x236/0x540 [btrfs] > btrfs_compress_pages+0xaa/0xf0 [btrfs] > compress_file_range+0x431/0x8e0 [btrfs] > async_cow_start+0x12/0x30 [btrfs] > btrfs_work_helper+0xf6/0x3e0 [btrfs] > process_one_work+0x294/0x5d0 > worker_thread+0x55/0x3c0 > kthread+0x140/0x170 > ret_from_fork+0x22/0x30 > ---[ end trace 63c3c0f131e61982 ]--- > > [CAUSE] > In lzo_compress_pages(), parameter @out_pages is not only an output > parameter (for the number of compressed pages), but also an input > parameter, as the upper limit of compressed pages we can utilize. > > In commit d4088803f511 ("btrfs: subpage: make lzo_compress_pages() > compatible"), the refactor doesn't take @out_pages as an input, thus > completely ignoring the limit. > > And for compress-force case, we could hit incompressible data that > compressed size would go beyond the page limit, and cause above crash. > > [FIX] > Save @out_pages as @max_nr_page, and pass it to lzo_compress_pages(), > and check if we're beyond the limit before accessing the pages. > > Reported-by: Omar Sandoval > Fixes: d4088803f511 ("btrfs: subpage: make lzo_compress_pages() compatible") > Signed-off-by: Qu Wenruo > Reviewed-by: Omar Sandoval > Reviewed-by: Josef Bacik Thanks, Josef