From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:45381 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750913AbeE3E61 (ORCPT ); Wed, 30 May 2018 00:58:27 -0400 Received: from relay2.suse.de (charybdis-ext-too.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 7D2C9ADFE for ; Wed, 30 May 2018 04:58:26 +0000 (UTC) From: Qu Wenruo To: linux-btrfs@vger.kernel.org Subject: [PATCH v4 3/4] btrfs: lzo: Add header length check to avoid slab out of bounds access Date: Wed, 30 May 2018 12:58:24 +0800 Message-Id: <20180530045824.11965-1-wqu@suse.com> In-Reply-To: <20180523082301.29874-4-wqu@suse.com> References: <20180523082301.29874-4-wqu@suse.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: James Harvey reported that some corrupted compressed extent data can lead to various kernel memory corruption. Such corrupted extent data belongs to inode with NODATASUM flags, thus data csum won't help us detecting such bug. If lucky enough, kasan could catch it like: ================================================================== BUG: KASAN: slab-out-of-bounds in lzo_decompress_bio+0x384/0x7a0 [btrfs] Write of size 4096 at addr ffff8800606cb0f8 by task kworker/u16:0/2338 CPU: 3 PID: 2338 Comm: kworker/u16:0 Tainted: G O 4.17.0-rc5-custom+ #50 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Workqueue: btrfs-endio btrfs_endio_helper [btrfs] Call Trace: dump_stack+0xc2/0x16b print_address_description+0x6a/0x270 kasan_report+0x260/0x380 memcpy+0x34/0x50 lzo_decompress_bio+0x384/0x7a0 [btrfs] end_compressed_bio_read+0x99f/0x10b0 [btrfs] bio_endio+0x32e/0x640 normal_work_helper+0x15a/0xea0 [btrfs] process_one_work+0x7e3/0x1470 worker_thread+0x1b0/0x1170 kthread+0x2db/0x390 ret_from_fork+0x22/0x40 ... ================================================================== The offending compressed data has the following info: Header: length 32768 (Looks completely valid) Segment 0 Header: length 3472882419 (Obvious out of bounds) Then when handling segment 0, since it's over the current page, we need the compressed data to workspace, then such large size would trigger out-of-bounds memory access, screwing up the whole kernel. Fix it by adding extra checks on header and segment headers to ensure we won't access out-of-bounds, and even checks the decompressed data won't be out-of-bounds. Reported-by: James Harvey Signed-off-by: Qu Wenruo --- changelog: v3->v4: Remove the incorrect decompression output length check. For compressed extent with offset, its cb->len is no longer the full uncompressed extent size. For decompressed size check, it's alraedy done in btrfs_decompress_buf2page(), thus we don't need this incorrect check here. Thanks Misono for pointing this out. --- fs/btrfs/lzo.c | 27 +++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c index ec5db393c758..995a96b51b38 100644 --- a/fs/btrfs/lzo.c +++ b/fs/btrfs/lzo.c @@ -293,6 +293,7 @@ static int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb) unsigned long working_bytes; size_t in_len; size_t out_len; + size_t max_segment_len = lzo1x_worst_compress(PAGE_SIZE); unsigned long in_offset; unsigned long in_page_bytes_left; unsigned long tot_in; @@ -306,10 +307,21 @@ static int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb) data_in = kmap(pages_in[0]); tot_len = read_compress_length(data_in); + /* + * Compressed data header check. + * + * The real compressed size can't exceed extent length, and all pages + * should be used (a full pending page is not possible). + * If this happens it means the compressed extent is corrupted. + */ + if (tot_len > min_t(size_t, BTRFS_MAX_COMPRESSED, srclen) || + tot_len < srclen - PAGE_SIZE) { + ret = -EUCLEAN; + goto done; + } tot_in = LZO_LEN; in_offset = LZO_LEN; - tot_len = min_t(size_t, srclen, tot_len); in_page_bytes_left = PAGE_SIZE - LZO_LEN; tot_out = 0; @@ -320,6 +332,17 @@ static int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb) in_offset += LZO_LEN; tot_in += LZO_LEN; + /* + * Segment header check. + * + * The segment length must not exceed max lzo compression + * size, nor the total compressed size + */ + if (in_len > max_segment_len || tot_in + in_len > tot_len) { + ret = -EUCLEAN; + goto done; + } + tot_in += in_len; working_bytes = in_len; may_late_unmap = need_unmap = false; @@ -370,7 +393,7 @@ static int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb) } } - out_len = lzo1x_worst_compress(PAGE_SIZE); + out_len = max_segment_len; ret = lzo1x_decompress_safe(buf, in_len, workspace->buf, &out_len); if (need_unmap) -- 2.17.0