[PATCH 1/2] Revert "xfrm: interface with if_id 0 should return error"

["Kai Lüke" <kailueke@linux.microsoft.com>]

This reverts commit 68ac0f3810e76a853b5f7b90601a05c3048b8b54 because it
breaks userspace (e.g., Cilium is affected because it used id 0 for the
dummy state https://github.com/cilium/cilium/pull/18789).

Signed-off-by: Kai Lueke <kailueke@linux.microsoft.com>
---
 net/xfrm/xfrm_user.c | 21 +++------------------
 1 file changed, 3 insertions(+), 18 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 8cd6c8129004..be89a8ac54a4 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -630,13 +630,8 @@ static struct xfrm_state
*xfrm_state_construct(struct net *net,
 
     xfrm_smark_init(attrs, &x->props.smark);
 
-    if (attrs[XFRMA_IF_ID]) {
+    if (attrs[XFRMA_IF_ID])
         x->if_id = nla_get_u32(attrs[XFRMA_IF_ID]);
-        if (!x->if_id) {
-            err = -EINVAL;
-            goto error;
-        }
-    }
 
     err = __xfrm_init_state(x, false, attrs[XFRMA_OFFLOAD_DEV]);
     if (err)
@@ -1432,13 +1427,8 @@ static int xfrm_alloc_userspi(struct sk_buff
*skb, struct nlmsghdr *nlh,
 
     mark = xfrm_mark_get(attrs, &m);
 
-    if (attrs[XFRMA_IF_ID]) {
+    if (attrs[XFRMA_IF_ID])
         if_id = nla_get_u32(attrs[XFRMA_IF_ID]);
-        if (!if_id) {
-            err = -EINVAL;
-            goto out_noput;
-        }
-    }
 
     if (p->info.seq) {
         x = xfrm_find_acq_byseq(net, mark, p->info.seq);
@@ -1751,13 +1741,8 @@ static struct xfrm_policy
*xfrm_policy_construct(struct net *net, struct xfrm_us
 
     xfrm_mark_get(attrs, &xp->mark);
 
-    if (attrs[XFRMA_IF_ID]) {
+    if (attrs[XFRMA_IF_ID])
         xp->if_id = nla_get_u32(attrs[XFRMA_IF_ID]);
-        if (!xp->if_id) {
-            err = -EINVAL;
-            goto error;
-        }
-    }
 
     return xp;
  error:
-- 
2.35.1