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

[Chao Yu <chao@kernel.org>]

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);