> On Apr 18, 2018, at 9:49 AM, Theodore Ts'o <tytso@xxxxxxx> wrote:
>
> If ext4 tries to start a reserved handle via
> jbd2_journal_start_reserved(), and the journal has been aborted, this
> can result in a NULL pointer dereference. This is because the fields
> h_journal and h_transaction in the handle structure share the same
> meory, via a union, so jbd2_journal_start_reserved() will clear
(typo) s/meory/memory/
Otherwise it looks fine. I was wondering if it would be safer to
check if (journal == NULL) in jbd2_journal_free_reserved(), but that
adds overhead for each caller, while your patch only adds the extra
code in the error case.
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> h_journal before calling start_this_handle(). If this function fails
> due to an aborted handle, h_journal will still be NULL, and the call
> to jbd2_journal_free_reserved() will pass a NULL journal to
> sub_reserve_credits().
>
> This can be reproduced by running "kvm-xfstests -c dioread_nolock
> generic/475".
>
> Fixes: 8f7d89f36829b ("jbd2: transaction reservation support")
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: stable@xxxxxxxxxx # 3.11
> ---
> fs/jbd2/transaction.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index ac311037d7a5..8aa453784402 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -532,6 +532,7 @@ int jbd2_journal_start_reserved(handle_t *handle, unsigned int type,
> */
> ret = start_this_handle(journal, handle, GFP_NOFS);
> if (ret < 0) {
> + handle->h_journal = journal;
> jbd2_journal_free_reserved(handle);
> return ret;
> }
> --
> 2.16.1.72.g5be1f00a9a
>
Cheers, Andreas
Attachment:
signature.asc
Description: Message signed with OpenPGP
