From: Deepanshu Kartikey Date: Thu, 30 Oct 2025 15:30:03 +0000 (+0300) Subject: ocfs2: validate cl_bpc in allocator inodes to prevent divide-by-zero X-Git-Tag: v6.19-rc1~70^2~98 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=93ce0ff117b0c468961d7c296a03ad57e1e8da9f;p=thirdparty%2Fkernel%2Flinux.git ocfs2: validate cl_bpc in allocator inodes to prevent divide-by-zero The chain allocator field cl_bpc (blocks per cluster) is read from disk and used in division operations without validation. A corrupted filesystem image with cl_bpc=0 causes a divide-by-zero crash in the kernel: divide error: 0000 [#1] PREEMPT SMP KASAN RIP: 0010:ocfs2_bg_discontig_add_extent fs/ocfs2/suballoc.c:335 [inline] RIP: 0010:ocfs2_block_group_fill+0x5bd/0xa70 fs/ocfs2/suballoc.c:386 Call Trace: ocfs2_block_group_alloc+0x7e9/0x1330 fs/ocfs2/suballoc.c:703 ocfs2_reserve_suballoc_bits+0x20a6/0x4640 fs/ocfs2/suballoc.c:834 ocfs2_reserve_new_inode+0x4f4/0xcc0 fs/ocfs2/suballoc.c:1074 ocfs2_mknod+0x83c/0x2050 fs/ocfs2/namei.c:306 This patch adds validation in ocfs2_validate_inode_block() to ensure cl_bpc matches the expected value calculated from the superblock's cluster size and block size for chain allocator inodes (identified by OCFS2_CHAIN_FL). Moving the validation to inode validation time (rather than allocation time) has several benefits: - Validates once when the inode is read, rather than on every allocation - Protects all code paths that use cl_bpc (allocation, resize, etc.) - Follows the existing pattern of inode validation in OCFS2 - Centralizes validation logic The validation catches both: - Zero values that cause divide-by-zero crashes - Non-zero but incorrect values indicating filesystem corruption or mismatched filesystem geometry With this fix, mounting a corrupted filesystem produces: OCFS2: ERROR (device loop0): ocfs2_validate_inode_block: Inode 74 has corrupted cl_bpc: ondisk=0 expected=16 instead of a kernel crash. [dmantipov@yandex.ru: combine into the series and tweak the message to fit the commonly used style] Link: https://lkml.kernel.org/r/20251030153003.1934585-2-dmantipov@yandex.ru Link: https://lore.kernel.org/ocfs2-devel/20251026132625.12348-1-kartikey406@gmail.com/T/#u [v1] Link: https://lore.kernel.org/all/20251027124131.10002-1-kartikey406@gmail.com/T/ [v2] Signed-off-by: Deepanshu Kartikey Signed-off-by: Dmitry Antipov Reported-by: syzbot+fd8af97c7227fe605d95@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=fd8af97c7227fe605d95 Tested-by: syzbot+fd8af97c7227fe605d95@syzkaller.appspotmail.com Suggested-by: Joseph Qi Reviewed-by: Joseph Qi Cc: Heming Zhao Cc: Joel Becker Cc: Jun Piao Cc: Junxiao Bi Cc: Mark Fasheh Signed-off-by: Andrew Morton --- diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c index 0f39ce0a2d463..8d6c106bcb98d 100644 --- a/fs/ocfs2/inode.c +++ b/fs/ocfs2/inode.c @@ -1515,6 +1515,8 @@ int ocfs2_validate_inode_block(struct super_block *sb, if (le32_to_cpu(di->i_flags) & OCFS2_CHAIN_FL) { struct ocfs2_chain_list *cl = &di->id2.i_chain; + u16 bpc = 1 << (OCFS2_SB(sb)->s_clustersize_bits - + sb->s_blocksize_bits); if (le16_to_cpu(cl->cl_count) != ocfs2_chain_recs_per_inode(sb)) { rc = ocfs2_error(sb, "Invalid dinode %llu: chain list count %u\n", @@ -1528,6 +1530,14 @@ int ocfs2_validate_inode_block(struct super_block *sb, le16_to_cpu(cl->cl_next_free_rec)); goto bail; } + if (OCFS2_SB(sb)->bitmap_blkno && + OCFS2_SB(sb)->bitmap_blkno != le64_to_cpu(di->i_blkno) && + le16_to_cpu(cl->cl_bpc) != bpc) { + rc = ocfs2_error(sb, "Invalid dinode %llu: bits per cluster %u\n", + (unsigned long long)bh->b_blocknr, + le16_to_cpu(cl->cl_bpc)); + goto bail; + } } rc = 0;