Re: [devel-ipsec] Re: [ipsec-next,v6,12/14] xfrm: add XFRM_MSG_MIGRATE_STATE for single SA migration

[Antony Antony <antony@phenome.org>]

Hi Simon,

On Wed, Mar 11, 2026 at 07:57:31PM +0000, Simon Horman via Devel wrote:
> This is an AI-generated review of your patch. The human sending this
> email has considered the AI review valid, or at least plausible.
> 
> For local reproduction steps see https://netdev-ai.bots.linux.dev/ai-local.html
> ---
> xfrm: add XFRM_MSG_MIGRATE_STATE for single SA migration
> 
> This patch adds a new netlink method to migrate a single xfrm_state.
> Unlike the existing migration mechanism (SA + policy), this supports
> migrating only the SA and allows changing the reqid.
> 
> > diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> > index 4b29ab92c2a7..ae2a1cf2311a 100644
> > --- a/include/net/xfrm.h
> > +++ b/include/net/xfrm.h
> > @@ -683,11 +683,17 @@ struct xfrm_migrate {
> >  	xfrm_address_t		new_daddr;
> >  	xfrm_address_t		new_saddr;
> >  	struct xfrm_encap_tmpl *encap;
> > -	struct xfrm_user_offload *xuo;
> > +	struct xfrm_user_offload xuo;
> 
> [ ... ]
> 
> > diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> > index 2f23ca5b62a9..de8b038fc08c 100644
> > --- a/net/xfrm/xfrm_policy.c
> > +++ b/net/xfrm/xfrm_policy.c
> > @@ -4642,6 +4642,19 @@ static int xfrm_migrate_check(const struct xfrm_migrate *m, int num_migrate,
> >  	return 0;
> >  }
> >
> > +/* Fill migrate fields that are invariant in XFRM_MSG_MIGRATE: inherited
> > + * from the existing SA unchanged.
> > + */
> > +static void xfrm_migrate_copy_old(struct xfrm_migrate *mp,
> > +				  const struct xfrm_state *x)
> > +{
> > +	mp->smark                  = x->props.smark;
> > +	mp->new_reqid              = x->props.reqid;
> > +	mp->nat_keepalive_interval = x->nat_keepalive_interval;
> > +	mp->mapping_maxage         = x->mapping_maxage;
> > +	mp->new_mark               = x->mark;
> > +}
> > +
> >  int xfrm_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
> >  		 struct xfrm_migrate *m, int num_migrate,
> >  		 struct xfrm_kmaddress *k, struct net *net,
> > @@ -4680,7 +4693,10 @@ int xfrm_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
> >  			x_cur[nx_cur] = x;
> >  			nx_cur++;
> >  			mp->encap = encap;
> > -			mp->xuo = xuo;
> > +			if (xuo)
> > +				mp->xuo = *xuo;
>                                      ^^^^
> >  			xfrm_migrate_copy_old(mp, x);
> >
> 
> What happens to mp->xuo when xuo is NULL?

thanks. I also red this on NIPA AI reviews. I will fix it in the next 
version.

> 
> The xfrm_migrate structure changed its xuo field from a pointer
> (struct xfrm_user_offload *xuo) to an embedded value
> (struct xfrm_user_offload xuo).
> 
> In xfrm_migrate(), when the xuo parameter is NULL (PF_KEY path via
> pfkey_migrate, or XFRM_MSG_MIGRATE without XFRMA_OFFLOAD_DEV), the
> 'if (xuo) mp->xuo = *xuo' branch is skipped, leaving mp->xuo with
> uninitialized stack data.
> 
> Both callers declare 'struct xfrm_migrate m[XFRM_MAX_DEPTH]' on the
> stack without zeroing:
> 
> net/key/af_key.c:pfkey_migrate() {
>     struct xfrm_migrate m[XFRM_MAX_DEPTH];
>     ...
>     err = xfrm_migrate(&sel, dir, XFRM_POLICY_TYPE_MAIN, m, i,
>                        k.local && k.remote ? &k : NULL, net,
>                        NULL, 0, NULL);
> }
> 
> net/xfrm/xfrm_user.c:xfrm_do_migrate() {
>     struct xfrm_migrate m[XFRM_MAX_DEPTH];

-  struct xfrm_migrate m[XFRM_MAX_DEPTH];
+  struct xfrm_migrate m[XFRM_MAX_DEPTH] = {};

this should fix it.

>     ...
>     err = xfrm_migrate(&sel, dir, type, m, n, k, net, encap, xuo, extack);
> }
> 
> The uninitialized mp->xuo.ifindex is later read in
> xfrm_state_migrate_create() and xfrm_state_migrate_install():
> 
> net/xfrm/xfrm_state.c:xfrm_state_migrate_create() {
>     ...
>     /* configure the hardware if offload is requested */
>     if (m->xuo.ifindex && xfrm_dev_state_add(net, xc, &m->xuo, extack))
>         goto error;
> }
> 
> net/xfrm/xfrm_state.c:xfrm_state_migrate_install() {
>     ...
>     if (xfrm_state_add(xc) < 0) {
>         NL_SET_ERR_MSG(extack, "Failed to add migrated state");
>         if (m->xuo.ifindex)
>             xfrm_dev_state_delete(xc);
>         ...
>     }
> }
> 
> If the stack garbage contains a non-zero ifindex value,
> xfrm_dev_state_add() will be called with random ifindex and flags,
> potentially causing spurious hardware offload attempts or migration
> failures.
> 
> Previously, 'mp->xuo = xuo' unconditionally set the pointer to NULL in
> these paths, which was then properly checked as 'if (m->xuo)'.
> 
> Should mp->xuo be zero-initialized when xuo is NULL, either by adding
> 'else memset(&mp->xuo, 0, sizeof(mp->xuo))' after the if-block, or by
> zero-initializing the m[] arrays in the callers?

thanks,
-antony