Re: [PATCH] ocfs2: revalidate the journal dinode before toggling dirty

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

On 5/9/26 9:52 PM, ZhengYuan Huang wrote:
> [BUG]
> A fuzzed OCFS2 image can corrupt the current slot journal dinode while
> mount is still in progress. The mount path first reports the invalid
> journal block and then crashes in shutdown:
> 
> kernel BUG at fs/ocfs2/journal.c:1034!
> Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
> RIP: 0010:ocfs2_journal_toggle_dirty+0x2d6/0x340 fs/ocfs2/journal.c:1034
> Call Trace:
>  ocfs2_journal_shutdown+0x414/0xc30 fs/ocfs2/journal.c:1116
>  ocfs2_mount_volume fs/ocfs2/super.c:1785 [inline]
>  ocfs2_fill_super+0x30a9/0x3cd0 fs/ocfs2/super.c:1083
>  get_tree_bdev_flags+0x38b/0x640 fs/super.c:1698
>  get_tree_bdev+0x24/0x40 fs/super.c:1721
>  ocfs2_get_tree+0x21/0x30 fs/ocfs2/super.c:1184
>  vfs_get_tree+0x9a/0x370 fs/super.c:1758
>  fc_mount fs/namespace.c:1199 [inline]
>  do_new_mount_fc fs/namespace.c:3642 [inline]
>  do_new_mount fs/namespace.c:3718 [inline]
>  path_mount+0x5b8/0x1ea0 fs/namespace.c:4028
>  do_mount fs/namespace.c:4041 [inline]
>  __do_sys_mount fs/namespace.c:4229 [inline]
>  __se_sys_mount fs/namespace.c:4206 [inline]
>  __x64_sys_mount+0x282/0x320 fs/namespace.c:4206
>  ...
> 
> 
> [CAUSE]
> ocfs2_journal_toggle_dirty() assumes journal->j_bh still contains the
> same validated dinode that ocfs2_journal_init() locked earlier, and it
> uses BUG_ON() when the buffer no longer looks like a dinode. That
> assumption is too strong. The mount path can force the same current-slot
> journal inode block back in from disk through
> ocfs2_read_journal_inode(..., OCFS2_BH_IGNORE_CACHE) while
> ocfs2_mark_dead_nodes() scans the journal slots. If that reread finds
> corrupted metadata, mount unwinds through ocfs2_journal_shutdown(),
> which reuses journal->j_bh and turns the metadata corruption into a
> kernel BUG.
> 

A bit confused.
Since journal dinode is firstly validated, it means image is checked.
Now mount is in progress, how to corrupt it during runtime?

Thanks,
Joseph

> [FIX]
> Revalidate journal->j_bh with ocfs2_validate_inode_block() before
> updating the dirty flag. If the cached journal dinode has become
> invalid, return the corruption error and keep the failure on OCFS2's
> normal read-only/error path instead of crashing the kernel. This
> revalidation happens in the cold path of mount, so the performance
> impact should be negligible.
> 
> Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
> ---
>  fs/ocfs2/journal.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
> index f9bf3bac085d..c9a972a1304e 100644
> --- a/fs/ocfs2/journal.c
> +++ b/fs/ocfs2/journal.c
> @@ -1021,12 +1021,15 @@ static int ocfs2_journal_toggle_dirty(struct ocfs2_super *osb,
>  	struct buffer_head *bh = journal->j_bh;
>  	struct ocfs2_dinode *fe;
>  
> -	fe = (struct ocfs2_dinode *)bh->b_data;
> +	/* The journal inode block can be forced back in from disk while the
> +	 * mount path is still running, so validate the cached bh again before
> +	 * updating the journal state on disk.
> +	 */
> +	status = ocfs2_validate_inode_block(osb->sb, bh);
> +	if (status < 0)
> +		return status;
>  
> -	/* The journal bh on the osb always comes from ocfs2_journal_init()
> -	 * and was validated there inside ocfs2_inode_lock_full().  It's a
> -	 * code bug if we mess it up. */
> -	BUG_ON(!OCFS2_IS_VALID_DINODE(fe));
> +	fe = (struct ocfs2_dinode *)bh->b_data;
>  
>  	flags = le32_to_cpu(fe->id1.journal1.ij_flags);
>  	if (dirty)