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([138.199.21.245]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b2d4dd83d5sm10249585ad.25.2026.04.09.20.00.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2026 20:00:21 -0700 (PDT) From: ZhengYuan Huang To: mark@fasheh.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com Cc: ocfs2-devel@lists.linux.dev, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, r33s3n6@gmail.com, zzzccc427@gmail.com, ZhengYuan Huang Subject: [PATCH v4] ocfs2: validate bg_bits during freefrag scan Date: Fri, 10 Apr 2026 11:00:04 +0800 Message-ID: <20260410030004.3810769-1-gality369@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit [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); + + /* + * 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++) { -- 2.43.0