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SubjectRe: [PATCH] ocfs2: fix crash issue if access released lockres in debugfs
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Hi,
Sorry for the late reply.
It seems it is indeed an issue and I'll get into it more deeply.
I'm curious about how you figure out this? Is it a real issue you've
encountered?

Thanks,
Joseph

On 9/20/22 3:36 PM, Rock Li wrote:
> Access locking_state of dlm debugfs may cause crash as scene below:
>
> Proc A: Proc that access debuginfo:
> add_lockres_tracking(lockresA)
> ...
> ocfs2_dlm_seq_next():
> //priv->p_iter_res points to next
> //lockres e.g. B. priv->p_tmp_res hold
> //copy of lockres A before leave
> ocfs2_dlm_seq_show()
> ...
> remove_lockres_tracking(lockres B):
> //free lockres B, l_debug_list in
> //priv->p_ter_res is updated but not
> //priv->p_tmp_res
> ...
> ocfs2_dlm_seq_next():
> //priv->p_tmp_res which holds a old copy of
> //lockres A, the l_debug_list holds a
> //out-of-date succeed pointer, which will
> //cause crash as //access invalid memory
> iter = v; //priv->p_tmp_res
> iter = ocfs2_dlm_next_res(iter, priv)
>
> The root cause of this issue is that private->p_iter_res acts as the
> agent of accessing lockres and is protected by ocfs2_dlm_tracking_lock
> while p_tmp_res is only a copy of the lockres and will be out-of-dated
> after leave critial region of ocfs2_dlm_tracking_lock. We should use
> priv->p_ter_res as the forward iterater instead.
>
> Signed-off-by: Rock Li <lihongweizz@inspur.com>
> ---
> fs/ocfs2/dlmglue.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index c28bc98..5d84350 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -3109,7 +3109,7 @@ static void *ocfs2_dlm_seq_next(struct seq_file *m, void *v, loff_t *pos)
> struct ocfs2_lock_res *dummy = &priv->p_iter_res;
>
> spin_lock(&ocfs2_dlm_tracking_lock);
> - iter = ocfs2_dlm_next_res(iter, priv);
> + iter = ocfs2_dlm_next_res(dummy, priv);
> list_del_init(&dummy->l_debug_list);
> if (iter) {
> list_add(&dummy->l_debug_list, &iter->l_debug_list);

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