Re: [PATCH net v2 1/1] xfrm: use hlist_del_init_rcu for state_cache and state_cache_input

On Thu, Jul 30, 2026 at 07:40:08PM +0800, Siwei Zhang wrote:
> From: Siwei Zhang <[email protected]>
> 
> Commit 14acf9652e56 ("xfrm: defensively unhash xfrm_state lists in
> __xfrm_state_delete") converted bydst/bysrc/byseq/byspi from
> hlist_del_rcu() to hlist_del_init_rcu() so that a second
> __xfrm_state_delete() on the same object becomes a no-op rather than a
> write through LIST_POISON pprev. It missed state_cache and
> state_cache_input, which kept hlist_del_rcu():
> 
> - hlist_del_rcu() leaves pprev = LIST_POISON2 (non-NULL), so
>   hlist_unhashed() returns false.
> - hlist_del_init_rcu() leaves pprev = NULL, so hlist_unhashed()
>   returns true.
> 
> A second __xfrm_state_delete() therefore enters __hlist_del() on the
> already-deleted state_cache/state_cache_input nodes and does
> WRITE_ONCE(*pprev, next) through LIST_POISON2 — a write use-after-free
> once the slab is reused. The corruption can in turn cause a subsequent
> hlist_for_each_entry_rcu traversal to follow a dangling next pointer,
> producing the read use-after-free reported in xfrm_input_state_lookup().
> 
> Switch state_cache and state_cache_input to hlist_del_init_rcu() to
> match the other four lists, closing the write use-after-free and, with
> it, the read use-after-free it spawns.
> 
> Assisted-by: CodeBuddy:GLM-5.2
> Fixes: 0045e3d80613 ("xfrm: Cache used outbound xfrm states at the policy.")
> Fixes: 81a331a0e72d ("xfrm: Add an inbound percpu state cache.")
> Cc: [email protected]
> Signed-off-by: Siwei Zhang <[email protected]>
> ---
>  net/xfrm/xfrm_state.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index 36a4f6793ede..f494c1ac57a4 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -823,9 +823,9 @@ int __xfrm_state_delete(struct xfrm_state *x)
>  		if (!hlist_unhashed(&x->byseq))
>  			hlist_del_init_rcu(&x->byseq);
>  		if (!hlist_unhashed(&x->state_cache))
> -			hlist_del_rcu(&x->state_cache);
> +			hlist_del_init_rcu(&x->state_cache);
>  		if (!hlist_unhashed(&x->state_cache_input))
> -			hlist_del_rcu(&x->state_cache_input);
> +			hlist_del_init_rcu(&x->state_cache_input);
>  
>  		if (!hlist_unhashed(&x->byspi))
>  			hlist_del_init_rcu(&x->byspi);

What is the difference between v1 and v2 of your patch?
Both look identical to me.