[bug report] netfilter: nf_tables: nft_set_rbtree: fix spurious insertion failure

[Dan Carpenter <error27@gmail.com>]

Hello Florian Westphal,

Commit 087388278e0f ("netfilter: nf_tables: nft_set_rbtree: fix
spurious insertion failure") from Sep 28, 2023 (linux-next), leads to
the following Smatch static checker warning:

	net/netfilter/nft_set_rbtree.c:399 __nft_rbtree_insert()
	warn: 'removed_end' is not an error pointer

net/netfilter/nft_set_rbtree.c
    379         /* Detect overlap by going through the list of valid tree nodes.
    380          * Values stored in the tree are in reversed order, starting from
    381          * highest to lowest value.
    382          */
    383         for (node = first; node != NULL; node = next) {
    384                 next = rb_next(node);
    385 
    386                 rbe = rb_entry(node, struct nft_rbtree_elem, node);
    387 
    388                 if (!nft_set_elem_active(&rbe->ext, genmask))
    389                         continue;
    390 
    391                 /* perform garbage collection to avoid bogus overlap reports
    392                  * but skip new elements in this transaction.
    393                  */
    394                 if (__nft_set_elem_expired(&rbe->ext, tstamp) &&
    395                     nft_set_elem_active(&rbe->ext, cur_genmask)) {
    396                         const struct nft_rbtree_elem *removed_end;
    397 
    398                         removed_end = nft_rbtree_gc_elem(set, priv, rbe);
--> 399                         if (IS_ERR(removed_end))
    400                                 return PTR_ERR(removed_end);

nft_rbtree_gc_elem() returns NULL, not error pointers.

    401 
    402                         if (removed_end == rbe_le || removed_end == rbe_ge)
    403                                 return -EAGAIN;
    404 
    405                         continue;
    406                 }

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regards,
dan carpenter