A corrupted filesystem image can have an inode allocator with the
OCFS2_BITMAP_FL flag incorrectly set, making ocfs2_is_cluster_bitmap()
return true. 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 have OCFS2_BITMAP_FL flag set
- Other allocators (inode, extent) must NOT have OCFS2_BITMAP_FL set

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
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 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

On 2026/1/4 09:40, Deepanshu Kartikey wrote:
> A corrupted filesystem image can have an inode allocator with the
> OCFS2_BITMAP_FL flag incorrectly set, making ocfs2_is_cluster_bitmap()
> return true. When the code later calls ocfs2_block_group_search(),
> it triggers BUG_ON(ocfs2_is_cluster_bitmap(inode)) causing a kernel panic.
> 
But ocfs2_is_cluster_bitmap() checks ip_blkno.

Thanks,
Joseph

> 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 have OCFS2_BITMAP_FL flag set
> - Other allocators (inode, extent) must NOT have OCFS2_BITMAP_FL set
> 
> 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
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> ---
>  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);
>

On Thu, Jan 8, 2026 at 1:55 PM Joseph Qi <joseph.qi@linux.alibaba.com> wrote:
>
>
>
> On 2026/1/4 09:40, Deepanshu Kartikey wrote:
> > A corrupted filesystem image can have an inode allocator with the
> > OCFS2_BITMAP_FL flag incorrectly set, making ocfs2_is_cluster_bitmap()
> > return true. When the code later calls ocfs2_block_group_search(),
> > it triggers BUG_ON(ocfs2_is_cluster_bitmap(inode)) causing a kernel panic.
> >
> But ocfs2_is_cluster_bitmap() checks ip_blkno.
>
> Thanks,
> Joseph
>

Hi Joseph,

Thanks for the correction. You're right, ocfs2_is_cluster_bitmap()
compares ip_blkno with osb->bitmap_blkno, not a flag.

I will send a v2 with the corrected commit message.

Thanks, Deepanshu