Re: [PATCH v2] ocfs2: validate allocator type to prevent BUG_ON in ocfs2_block_group_search

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 1/23/26 2:23 PM, Deepanshu Kartikey wrote:
> On Sat, Jan 10, 2026 at 11:14 AM Deepanshu Kartikey
> <kartikey406@gmail.com> wrote:
>>
>> ocfs2_is_cluster_bitmap() checks whether an inode is the global bitmap
>> by comparing ip_blkno with osb->bitmap_blkno. A corrupted filesystem
>> can have either the superblock's bitmap_blkno field corrupted to point
>> to the inode allocator block, or the inode allocator's i_blkno field
>> corrupted to match bitmap_blkno. In either case, ocfs2_is_cluster_bitmap()
>> returns true for the inode allocator.
>>
>> When the code later calls ocfs2_block_group_search(), it triggers
>> BUG_ON(ocfs2_is_cluster_bitmap(inode)) causing a kernel panic.
>>
>> Call trace:
>>   ocfs2_block_group_search+0x1c7/0x2c0 fs/ocfs2/suballoc.c:1611
>>   ocfs2_search_chain+0x38a/0x1010 fs/ocfs2/suballoc.c:1764
>>   ocfs2_claim_suballoc_bits+0x3a4/0x650 fs/ocfs2/suballoc.c:1978
>>   ocfs2_claim_new_inode+0x95/0x130 fs/ocfs2/suballoc.c:2137
>>   ocfs2_mknod_locked+0x129/0x510 fs/ocfs2/namei.c:568
>>   ocfs2_mknod+0x5c7/0x11d0 fs/ocfs2/namei.c:802
>>   ocfs2_create+0x136/0x170 fs/ocfs2/namei.c:852
>>
>> Add validation in ocfs2_reserve_suballoc_bits() to check that the
>> allocator inode type matches the expected type:
>> - Global bitmap allocator must be the cluster bitmap
>> - Other allocators (inode, extent) must NOT be the cluster bitmap
>>
>> This follows the existing pattern of validating OCFS2_CHAIN_FL in the
>> same function and uses ocfs2_error() for graceful error handling.
>>
>> Reported-by: syzbot+44c564a3cb08605f34a1@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=44c564a3cb08605f34a1
>> Tested-by: syzbot+44c564a3cb08605f34a1@syzkaller.appspotmail.com
>> Link: https://lore.kernel.org/all/20260104014028.305029-1-kartikey406@gmail.com/T/ [v1]
>> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
>> ---
>> v2: Fix commit message - ocfs2_is_cluster_bitmap() checks ip_blkno
>>     against bitmap_blkno, not a flag (Joseph Qi)
>> ---
>>  fs/ocfs2/suballoc.c | 20 ++++++++++++++++++++
>>  1 file changed, 20 insertions(+)
>>
>> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
>> index 8e6e5235b30c..fb72c062a8d5 100644
>> --- a/fs/ocfs2/suballoc.c
>> +++ b/fs/ocfs2/suballoc.c
>> @@ -813,6 +813,26 @@ static int ocfs2_reserve_suballoc_bits(struct ocfs2_super *osb,
>>                 goto bail;
>>         }
>>
>> +       /*
>> +        * Validate allocator type matches expected bitmap type.
>> +        * Global bitmap must have BITMAP flag, other allocators must not.
>> +        * This prevents a corrupted filesystem from triggering BUG_ON
>> +        * in ocfs2_block_group_search() or ocfs2_cluster_group_search().
>> +        */
>> +       if (type == GLOBAL_BITMAP_SYSTEM_INODE) {
>> +               if (!ocfs2_is_cluster_bitmap(alloc_inode)) {
>> +                       status = ocfs2_error(alloc_inode->i_sb,
>> +                                            "Global bitmap %llu missing bitmap flag\n",
>> +                                            (unsigned long long)le64_to_cpu(fe->i_blkno));
>> +                       goto bail;
>> +               }
>> +       } else if (ocfs2_is_cluster_bitmap(alloc_inode)) {
>> +               status = ocfs2_error(alloc_inode->i_sb,
>> +                                    "Allocator %llu has invalid bitmap flag\n",
>> +                                    (unsigned long long)le64_to_cpu(fe->i_blkno));
>> +               goto bail;
>> +       }
>> +
>>         free_bits = le32_to_cpu(fe->id1.bitmap1.i_total) -
>>                 le32_to_cpu(fe->id1.bitmap1.i_used);
>>
>> --
>> 2.43.0
>>
> 
> 
> Hi Joseph,
> 
> Just wanted to follow up on this patch. Do you have any further
> comments or suggestions?
> 
Hi，since the inode block is read from disk, it seems we'd better
validate it in ocfs2_validate_inode_block().

Thanks,
Joseph