linux-kernel - Re: [PATCH v2] ocfs2: validate allocator type to prevent BUG_ON in ocfs2_block_group

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Message-ID: <CADhLXY6Dojpckbkq7Dk_T7BrHML9_AAscJ+xKt3aPiV9v1V73w@mail.gmail.com>
Date: Fri, 23 Jan 2026 11:53:46 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: mark@...heh.com, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com
Cc: ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	syzbot+44c564a3cb08605f34a1@...kaller.appspotmail.com
Subject: Re: [PATCH v2] ocfs2: validate allocator type to prevent BUG_ON in ocfs2_block_group_search

On Sat, Jan 10, 2026 at 11:14 AM Deepanshu Kartikey
<kartikey406@...il.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@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=44c564a3cb08605f34a1
> Tested-by: syzbot+44c564a3cb08605f34a1@...kaller.appspotmail.com
> Link: https://lore.kernel.org/all/20260104014028.305029-1-kartikey406@gmail.com/T/ [v1]
> Signed-off-by: Deepanshu Kartikey <kartikey406@...il.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?

Thanks,
Deepanshu