Re: [PATCH] f2fs: validate orphan inode entry count

[Chao Yu <chao@kernel.org>]

On 5/26/26 13:38, Wenjie Qi wrote:
> Agreed, SBI_NEED_FSCK may not be persisted at this stage.
> 
>   I sent v2 to add ERROR_INCONSISTENT_ORPHAN and call f2fs_handle_error() on
>   invalid orphan entry_count, so the corruption reason can be recorded in
>   s_errors[] as a persistent hint for fsck.

So, it needs another patch to let fsck recognize the new flag?

Thanks,

> 
> https://lore.kernel.org/linux-f2fs-devel/20260526053557.1096229-1-qiwenjie@xiaomi.com/T/#u
> 
> On Tue, May 26, 2026 at 10:19 AM Chao Yu <chao@kernel.org> wrote:
>>
>> On 5/25/26 19:46, Wenjie Qi wrote:
>>> f2fs_recover_orphan_inodes() trusts the orphan block entry_count when
>>> replaying orphan inodes from the checkpoint pack.  A corrupted
>>> entry_count larger than F2FS_ORPHANS_PER_BLOCK makes the recovery loop
>>> read past the ino[] array and interpret footer or following data as
>>> inode numbers.
>>>
>>> On a crafted image, mounting an unpatched kernel can drive orphan
>>> recovery into f2fs_bug_on() and panic the kernel.  Validate entry_count
>>> before consuming entries so corrupted checkpoint data fails the mount
>>> with -EFSCORRUPTED and requests fsck instead.
>>>
>>> Fixes: 127e670abfa7 ("f2fs: add checkpoint operations")
>>> Cc: stable@kernel.org
>>> Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
>>> ---
>>>  fs/f2fs/checkpoint.c | 13 ++++++++++++-
>>>  1 file changed, 12 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>> index c00a6b6ebcbd..fc72b69ff769 100644
>>> --- a/fs/f2fs/checkpoint.c
>>> +++ b/fs/f2fs/checkpoint.c
>>> @@ -943,6 +943,7 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
>>>       for (i = 0; i < orphan_blocks; i++) {
>>>               struct folio *folio;
>>>               struct f2fs_orphan_block *orphan_blk;
>>> +             unsigned int entry_count;
>>>
>>>               folio = f2fs_get_meta_folio(sbi, start_blk + i);
>>>               if (IS_ERR(folio)) {
>>> @@ -951,7 +952,17 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
>>>               }
>>>
>>>               orphan_blk = folio_address(folio);
>>> -             for (j = 0; j < le32_to_cpu(orphan_blk->entry_count); j++) {
>>> +             entry_count = le32_to_cpu(orphan_blk->entry_count);
>>> +             if (entry_count > F2FS_ORPHANS_PER_BLOCK) {
>>> +                     f2fs_err(sbi, "invalid orphan inode entry count %u",
>>> +                              entry_count);
>>> +                     set_sbi_flag(sbi, SBI_NEED_FSCK);
>>
>> Well, at this stage, I guess there is no chance to persist SBI_NEED_FSCK flag,
>> what about introduce ERROR_INCONSISTENT_ORPHAN in enum f2fs_error, so that
>> we can persist the new bit to provide hint to fsck?
>>
>> Thanks,
>>
>>> +                     err = -EFSCORRUPTED;
>>> +                     f2fs_folio_put(folio, true);
>>> +                     goto out;
>>> +             }
>>> +
>>> +             for (j = 0; j < entry_count; j++) {
>>>                       nid_t ino = le32_to_cpu(orphan_blk->ino[j]);
>>>
>>>                       err = recover_orphan_inode(sbi, ino);
>>