[lvc-project] [PATCH 2/2] ocfs2: validate cl_bpc in allocator inodes to prevent divide-by-zero

[Dmitry Antipov]

On 10/30/25 7:22 AM, Heming Zhao wrote:

> One way I considered uses the inode block number to bypass global_bitmap.
> the code seems ugly (demo):
> 
> ```
> osb = OCFS2_SB(sb);
> inode = ocfs2_get_system_file_inode(osb, GLOBAL_BITMAP_SYSTEM_INODE, OCFS2_INVALID_SLOT)
> 
> if (OCFS2_I(inode)->ip_blkno != le64_to_cpu(fe->i_blkno))
>    goto by_pass_the_check;

This is what happens in ocfs2_initialize_super(), and, IIUC, the global (cluster) bitmap
is the only dinode which can have cl_bpc set to 1. So what about the following:

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 709afbfd1f9f..a8138c150d81 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1520,7 +1520,18 @@ int ocfs2_validate_inode_block(struct super_block *sb,
                                          le16_to_cpu(cl->cl_next_free_rec));
                         goto bail;
                 }
-               if (le16_to_cpu(cl->cl_bpc) != bpc) {
+
+               if (OCFS2_SB(sb)->bitmap_blkno == 0 && le16_to_cpu(cl->cl_bpc) == 1)
+                       /* This dinode represents a cluster bitmap, and we're reading
+                        * it for the first time from ocfs2_initialize_super().
+                        */
+                       ;
+               else if (OCFS2_SB(sb)->bitmap_blkno == le64_to_cpu(di->i_blkno))
+                       /* This dinode represents a cluster bitmap, and we can
+                        * recognize it by using the known block number.
+                        */
+                       ;
+               else if (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));

Dmitry