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Received: from 30.221.145.28(mailfrom:joseph.qi@linux.alibaba.com fp:SMTPD_---0X0joJ7B_1775791394 cluster:ay36) by smtp.aliyun-inc.com; Fri, 10 Apr 2026 11:23:15 +0800 Message-ID: <45706dfa-6a4c-4e62-bddb-cebd206e469f@linux.alibaba.com> Date: Fri, 10 Apr 2026 11:23:14 +0800 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: [PATCH v4] ocfs2: validate bg_bits during freefrag scan To: ZhengYuan Huang , Heming Zhao Cc: ocfs2-devel@lists.linux.dev, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, r33s3n6@gmail.com, zzzccc427@gmail.com, Mark Fasheh , Joel Becker References: <20260410030004.3810769-1-gality369@gmail.com> From: Joseph Qi In-Reply-To: <20260410030004.3810769-1-gality369@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/10/26 11:00 AM, ZhengYuan Huang wrote: > [BUG] > A crafted filesystem can trigger an out-of-bounds bitmap walk when > OCFS2_IOC_INFO is issued with OCFS2_INFO_FL_NON_COHERENT. > > BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline] > BUG: KASAN: use-after-free in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline] > BUG: KASAN: use-after-free in test_bit_le include/asm-generic/bitops/le.h:21 [inline] > BUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline] > BUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline] > BUG: KASAN: use-after-free in ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline] > BUG: KASAN: use-after-free in ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754 > Read of size 8 at addr ffff888031bce000 by task syz.0.636/1435 > Call Trace: > __dump_stack lib/dump_stack.c:94 [inline] > dump_stack_lvl+0xbe/0x130 lib/dump_stack.c:120 > print_address_description mm/kasan/report.c:378 [inline] > print_report+0xd1/0x650 mm/kasan/report.c:482 > kasan_report+0xfb/0x140 mm/kasan/report.c:595 > check_region_inline mm/kasan/generic.c:186 [inline] > kasan_check_range+0x11c/0x200 mm/kasan/generic.c:200 > __kasan_check_read+0x11/0x20 mm/kasan/shadow.c:31 > instrument_atomic_read include/linux/instrumented.h:68 [inline] > _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline] > test_bit_le include/asm-generic/bitops/le.h:21 [inline] > ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline] > ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline] > ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline] > ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754 > ocfs2_info_handle+0x18d/0x2a0 fs/ocfs2/ioctl.c:828 > ocfs2_ioctl+0x632/0x6e0 fs/ocfs2/ioctl.c:913 > vfs_ioctl fs/ioctl.c:51 [inline] > __do_sys_ioctl fs/ioctl.c:597 [inline] > __se_sys_ioctl fs/ioctl.c:583 [inline] > __x64_sys_ioctl+0x197/0x1e0 fs/ioctl.c:583 > ... > > [CAUSE] > ocfs2_info_freefrag_scan_chain() uses on-disk bg_bits directly as the > bitmap scan limit. The coherent path reads group descriptors through > ocfs2_read_group_descriptor(), which validates the descriptor before > use. The non-coherent path uses ocfs2_read_blocks_sync() instead and > skips that validation, so an impossible bg_bits value can drive the > bitmap walk past the end of the block. > > [FIX] > Compute the bitmap capacity from the filesystem format with > ocfs2_group_bitmap_size(), report descriptors whose bg_bits exceeds > that limit, and clamp the scan to the computed capacity. This keeps the > freefrag report going while avoiding reads beyond the buffer. > > Fixes: d24a10b9f8ed ("Ocfs2: Add a new code 'OCFS2_INFO_FREEFRAG' for o2info ioctl.") > Signed-off-by: ZhengYuan Huang > --- > v4: > - add the freefrag introduction commit as a Fixes tag > - use cluster allocator bitmap sizing with ocfs2_group_bitmap_size(..., 0, ...) > - drop the unnecessary 8U suffix and tighten the mlog() formatting > > v3: > - restore the empty-group fast path before computing bitmap limits > - move the bg_bits clamp below bg_free_bits_count to skip extra work > for empty groups > > v2: > - use ocfs2_group_bitmap_size() instead of the on-disk bg_size field > - clamp bg_bits to the computed bitmap capacity and continue scanning > --- > fs/ocfs2/ioctl.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/fs/ocfs2/ioctl.c b/fs/ocfs2/ioctl.c > index b6864602814c..82d8e69dd575 100644 > --- a/fs/ocfs2/ioctl.c > +++ b/fs/ocfs2/ioctl.c > @@ -441,7 +441,7 @@ static int ocfs2_info_freefrag_scan_chain(struct ocfs2_super *osb, > struct buffer_head *bh = NULL; > struct ocfs2_group_desc *bg = NULL; > > - unsigned int max_bits, num_clusters; > + unsigned int max_bits, max_bitmap_bits, num_clusters; > unsigned int offset = 0, cluster, chunk; > unsigned int chunk_free, last_chunksize = 0; > > @@ -474,11 +474,26 @@ static int ocfs2_info_freefrag_scan_chain(struct ocfs2_super *osb, > } > > bg = (struct ocfs2_group_desc *)bh->b_data; > - > if (!le16_to_cpu(bg->bg_free_bits_count)) > continue; > > max_bits = le16_to_cpu(bg->bg_bits); > + max_bitmap_bits = 8 * > + ocfs2_group_bitmap_size(osb->sb, 0, > + osb->s_feature_incompat); > + max_bitmap_bits is unchanged, so it could be moved out of loop. Other looks good me. Thanks, Joseph > + /* > + * Non-coherent scans read raw blocks and do not get the > + * bg_bits validation from > + * ocfs2_read_group_descriptor(). > + */ > + if (max_bits > max_bitmap_bits) { > + mlog(ML_ERROR, > + "Group desc #%llu has %u bits, max bitmap bits %u\n", > + (unsigned long long)blkno, max_bits, max_bitmap_bits); > + max_bits = max_bitmap_bits; > + } > + > offset = 0; > > for (chunk = 0; chunk < chunks_in_group; chunk++) {