Re: [PATCH] jbd2: user-memory-access in jbd2__journal_start

[Jan Kara]

On Wed 31-01-24 20:04:27, Edward Adam Davis wrote:
> Before reusing the handle, it is necessary to confirm that the transaction is 
> ready.
> 
> Reported-and-tested-by: syzbot+cdee56dbcdf0096ef605@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>

Sorry but no. Dave found a way to fix this particular problem in XFS and
your patch would not really improve anything because we'd just crash
when dereferencing handle->saved_alloc_context.

								Honza


> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index cb0b8d6fc0c6..702312cd5392 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -493,6 +493,9 @@ handle_t *jbd2__journal_start(journal_t *journal, int nblocks, int rsv_blocks,
>  		return ERR_PTR(-EROFS);
>  
>  	if (handle) {
> +		if (handle->saved_alloc_context & ~PF_MEMALLOC_NOFS)
> +			return ERR_PTR(-EBUSY);
> +
>  		J_ASSERT(handle->h_transaction->t_journal == journal);
>  		handle->h_ref++;
>  		return handle;
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR