netfilter: nf_tables: clone set on flush only

Syzbot with fault injection triggered a failing memory allocation with
GFP_KERNEL which results in a WARN splat:

iter.err
WARNING: net/netfilter/nf_tables_api.c:845 at nft_map_deactivate+0x34e/0x3c0 net/netfilter/nf_tables_api.c:845, CPU#0: syz.0.17/5992
Modules linked in:
CPU: 0 UID: 0 PID: 5992 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:nft_map_deactivate+0x34e/0x3c0 net/netfilter/nf_tables_api.c:845
Code: 8b 05 86 5a 4e 09 48 3b 84 24 a0 00 00 00 75 62 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 63 6d fa f7 90 <0f> 0b 90 43
+80 7c 35 00 00 0f 85 23 fe ff ff e9 26 fe ff ff 89 d9
RSP: 0018:ffffc900045af780 EFLAGS: 00010293
RAX: ffffffff89ca45bd RBX: 00000000fffffff4 RCX: ffff888028111e40
RDX: 0000000000000000 RSI: 00000000fffffff4 RDI: 0000000000000000
RBP: ffffc900045af870 R08: 0000000000400dc0 R09: 00000000ffffffff
R10: dffffc0000000000 R11: fffffbfff1d141db R12: ffffc900045af7e0
R13: 1ffff920008b5f24 R14: dffffc0000000000 R15: ffffc900045af920
FS:  000055557a6a5500(0000) GS:ffff888125496000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb5ea271fc0 CR3: 000000003269e000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __nft_release_table+0xceb/0x11f0 net/netfilter/nf_tables_api.c:12115
 nft_rcv_nl_event+0xc25/0xdb0 net/netfilter/nf_tables_api.c:12187
 notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
 blocking_notifier_call_chain+0x6a/0x90 kernel/notifier.c:380
 netlink_release+0x123b/0x1ad0 net/netlink/af_netlink.c:761
 __sock_release net/socket.c:662 [inline]
 sock_close+0xc3/0x240 net/socket.c:1455

Restrict set clone to the flush set command in the preparation phase.
Add NFT_ITER_UPDATE_CLONE and use it for this purpose, update the rbtree
and pipapo backends to only clone the set when this iteration type is
used.

As for the existing NFT_ITER_UPDATE type, update the pipapo backend to
use the existing set clone if available, otherwise use the existing set
representation. After this update, there is no need to clone a set that
is being deleted, this includes bound anonymous set.

An alternative approach to NFT_ITER_UPDATE_CLONE is to add a .clone
interface and call it from the flush set path.

Reported-by: [email protected]
Fixes: 3f1d886 ("netfilter: nft_set_pipapo: move cloning of match info to insert/removal path")
Signed-off-by: Pablo Neira Ayuso <[email protected]>
Signed-off-by: Florian Westphal <[email protected]>

Author: ummakynes

include/net/netfilter/nf_tables.h

@@ -320,11 +320,13 @@ static inline void *nft_elem_priv_cast(const struct nft_elem_priv *priv)
  * @NFT_ITER_UNSPEC: unspecified, to catch errors
  * @NFT_ITER_READ: read-only iteration over set elements
  * @NFT_ITER_UPDATE: iteration under mutex to update set element state
+ * @NFT_ITER_UPDATE_CLONE: clone set before iteration under mutex to update element
  */
 enum nft_iter_type {
 	NFT_ITER_UNSPEC,
 	NFT_ITER_READ,
 	NFT_ITER_UPDATE,
+	NFT_ITER_UPDATE_CLONE,
 };
 
 struct nft_set;

net/netfilter/nf_tables_api.c

@@ -833,6 +833,11 @@ static void nft_map_catchall_deactivate(const struct nft_ctx *ctx,
 	}
 }
 
+/* Use NFT_ITER_UPDATE iterator even if this may be called from the preparation
+ * phase, the set clone might already exist from a previous command, or it might
+ * be a set that is going away and does not require a clone. The netns and
+ * netlink release paths also need to work on the live set.
+ */
 static void nft_map_deactivate(const struct nft_ctx *ctx, struct nft_set *set)
 {
 	struct nft_set_iter iter = {
@@ -7903,9 +7908,12 @@ static int nft_set_catchall_flush(const struct nft_ctx *ctx,
 
 static int nft_set_flush(struct nft_ctx *ctx, struct nft_set *set, u8 genmask)
 {
+	/* The set backend might need to clone the set, do it now from the
+	 * preparation phase, use NFT_ITER_UPDATE_CLONE iterator type.
+	 */
 	struct nft_set_iter iter = {
 		.genmask	= genmask,
-		.type		= NFT_ITER_UPDATE,
+		.type		= NFT_ITER_UPDATE_CLONE,
 		.fn		= nft_setelem_flush,
 	};
 

net/netfilter/nft_set_hash.c

@@ -374,6 +374,7 @@ static void nft_rhash_walk(const struct nft_ctx *ctx, struct nft_set *set,
 {
 	switch (iter->type) {
 	case NFT_ITER_UPDATE:
+	case NFT_ITER_UPDATE_CLONE:
 		/* only relevant for netlink dumps which use READ type */
 		WARN_ON_ONCE(iter->skip != 0);
 

net/netfilter/nft_set_pipapo.c

@@ -2144,13 +2144,20 @@ static void nft_pipapo_walk(const struct nft_ctx *ctx, struct nft_set *set,
 	const struct nft_pipapo_match *m;
 
 	switch (iter->type) {
-	case NFT_ITER_UPDATE:
+	case NFT_ITER_UPDATE_CLONE:
 		m = pipapo_maybe_clone(set);
 		if (!m) {
 			iter->err = -ENOMEM;
 			return;
 		}
-
+		nft_pipapo_do_walk(ctx, set, m, iter);
+		break;
+	case NFT_ITER_UPDATE:
+		if (priv->clone)
+			m = priv->clone;
+		else
+			m = rcu_dereference_protected(priv->match,
+						      nft_pipapo_transaction_mutex_held(set));
 		nft_pipapo_do_walk(ctx, set, m, iter);
 		break;
 	case NFT_ITER_READ:

net/netfilter/nft_set_rbtree.c

@@ -861,13 +861,15 @@ static void nft_rbtree_walk(const struct nft_ctx *ctx,
 	struct nft_rbtree *priv = nft_set_priv(set);
 
 	switch (iter->type) {
-	case NFT_ITER_UPDATE:
-		lockdep_assert_held(&nft_pernet(ctx->net)->commit_mutex);
-
+	case NFT_ITER_UPDATE_CLONE:
 		if (nft_array_may_resize(set) < 0) {
 			iter->err = -ENOMEM;
 			break;
 		}
+		fallthrough;
+	case NFT_ITER_UPDATE:
+		lockdep_assert_held(&nft_pernet(ctx->net)->commit_mutex);
+
 		nft_rbtree_do_walk(ctx, set, iter);
 		break;
 	case NFT_ITER_READ: