[SRU][J][PATCH 2/2] netfilter: nft_set_pipapo: split gc into unlink and reclaim phase
Tim Whisonant
tim.whisonant at canonical.com
Wed Apr 1 21:59:49 UTC 2026
From: Florian Westphal <fw at strlen.de>
commit 9df95785d3d8302f7c066050117b04cd3c2048c2 upstream.
Yiming Qian reports Use-after-free in the pipapo set type:
Under a large number of expired elements, commit-time GC can run for a very
long time in a non-preemptible context, triggering soft lockup warnings and
RCU stall reports (local denial of service).
We must split GC in an unlink and a reclaim phase.
We cannot queue elements for freeing until pointers have been swapped.
Expired elements are still exposed to both the packet path and userspace
dumpers via the live copy of the data structure.
call_rcu() does not protect us: dump operations or element lookups starting
after call_rcu has fired can still observe the free'd element, unless the
commit phase has made enough progress to swap the clone and live pointers
before any new reader has picked up the old version.
This a similar approach as done recently for the rbtree backend in commit
35f83a75529a ("netfilter: nft_set_rbtree: don't gc elements on insert").
Fixes: 3c4287f62044 ("nf_tables: Add set type for arbitrary concatenation of ranges")
Reported-by: Yiming Qian <yimingqian591 at gmail.com>
Signed-off-by: Florian Westphal <fw at strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 16f3595c0441d87dfa005c47d8f95be213afaa9e linux-6.1.y)
CVE-2026-23351
Signed-off-by: Tim Whisonant <tim.whisonant at canonical.com>
---
include/net/netfilter/nf_tables.h | 5 +++
net/netfilter/nf_tables_api.c | 5 ---
net/netfilter/nft_set_pipapo.c | 51 ++++++++++++++++++++++++++-----
net/netfilter/nft_set_pipapo.h | 2 ++
4 files changed, 50 insertions(+), 13 deletions(-)
diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 1296dbcf675ec..c5c612df73d36 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -1655,6 +1655,11 @@ struct nft_trans_gc {
struct rcu_head rcu;
};
+static inline int nft_trans_gc_space(const struct nft_trans_gc *trans)
+{
+ return NFT_TRANS_GC_BATCHCOUNT - trans->count;
+}
+
struct nft_trans_gc *nft_trans_gc_alloc(struct nft_set *set,
unsigned int gc_seq, gfp_t gfp);
void nft_trans_gc_destroy(struct nft_trans_gc *trans);
diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 49fc22db42d62..53a9baf03a628 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -9178,11 +9178,6 @@ static void nft_trans_gc_queue_work(struct nft_trans_gc *trans)
schedule_work(&trans_gc_work);
}
-static int nft_trans_gc_space(struct nft_trans_gc *trans)
-{
- return NFT_TRANS_GC_BATCHCOUNT - trans->count;
-}
-
struct nft_trans_gc *nft_trans_gc_queue_async(struct nft_trans_gc *gc,
unsigned int gc_seq, gfp_t gfp)
{
diff --git a/net/netfilter/nft_set_pipapo.c b/net/netfilter/nft_set_pipapo.c
index 12e077fb8f4e8..6ab5b59ee69cf 100644
--- a/net/netfilter/nft_set_pipapo.c
+++ b/net/netfilter/nft_set_pipapo.c
@@ -1577,11 +1577,11 @@ static void nft_pipapo_gc_deactivate(struct net *net, struct nft_set *set,
}
/**
- * pipapo_gc() - Drop expired entries from set, destroy start and end elements
+ * pipapo_gc_scan() - Drop expired entries from set and link them to gc list
* @set: nftables API set representation
* @m: Matching data
*/
-static void pipapo_gc(struct nft_set *set, struct nft_pipapo_match *m)
+static void pipapo_gc_scan(struct nft_set *set, struct nft_pipapo_match *m)
{
struct nft_pipapo *priv = nft_set_priv(set);
struct net *net = read_pnet(&set->net);
@@ -1594,6 +1594,8 @@ static void pipapo_gc(struct nft_set *set, struct nft_pipapo_match *m)
if (!gc)
return;
+ list_add(&gc->list, &priv->gc_head);
+
while ((rules_f0 = pipapo_rules_same_key(m->f, first_rule))) {
union nft_pipapo_map_bucket rulemap[NFT_PIPAPO_MAX_FIELDS];
const struct nft_pipapo_field *f;
@@ -1623,9 +1625,13 @@ static void pipapo_gc(struct nft_set *set, struct nft_pipapo_match *m)
if (__nft_set_elem_expired(&e->ext, tstamp)) {
priv->dirty = true;
- gc = nft_trans_gc_queue_sync(gc, GFP_ATOMIC);
- if (!gc)
- return;
+ if (!nft_trans_gc_space(gc)) {
+ gc = nft_trans_gc_alloc(set, 0, GFP_KERNEL);
+ if (!gc)
+ return;
+
+ list_add(&gc->list, &priv->gc_head);
+ }
nft_pipapo_gc_deactivate(net, set, e);
pipapo_drop(m, rulemap);
@@ -1639,10 +1645,30 @@ static void pipapo_gc(struct nft_set *set, struct nft_pipapo_match *m)
}
}
- gc = nft_trans_gc_catchall_sync(gc);
+ priv->last_gc = jiffies;
+}
+
+/**
+ * pipapo_gc_queue() - Free expired elements
+ * @set: nftables API set representation
+ */
+static void pipapo_gc_queue(struct nft_set *set)
+{
+ struct nft_pipapo *priv = nft_set_priv(set);
+ struct nft_trans_gc *gc, *next;
+
+ /* always do a catchall cycle: */
+ gc = nft_trans_gc_alloc(set, 0, GFP_KERNEL);
if (gc) {
+ gc = nft_trans_gc_catchall_sync(gc);
+ if (gc)
+ nft_trans_gc_queue_sync_done(gc);
+ }
+
+ /* always purge queued gc elements. */
+ list_for_each_entry_safe(gc, next, &priv->gc_head, list) {
+ list_del(&gc->list);
nft_trans_gc_queue_sync_done(gc);
- priv->last_gc = jiffies;
}
}
@@ -1696,6 +1722,10 @@ static void pipapo_reclaim_match(struct rcu_head *rcu)
*
* We also need to create a new working copy for subsequent insertions and
* deletions.
+ *
+ * After the live copy has been replaced by the clone, we can safely queue
+ * expired elements that have been collected by pipapo_gc_scan() for
+ * memory reclaim.
*/
static void nft_pipapo_commit(struct nft_set *set)
{
@@ -1703,7 +1733,7 @@ static void nft_pipapo_commit(struct nft_set *set)
struct nft_pipapo_match *new_clone, *old;
if (time_after_eq(jiffies, priv->last_gc + nft_set_gc_interval(set)))
- pipapo_gc(set, priv->clone);
+ pipapo_gc_scan(set, priv->clone);
if (!priv->dirty)
return;
@@ -1720,6 +1750,8 @@ static void nft_pipapo_commit(struct nft_set *set)
call_rcu(&old->rcu, pipapo_reclaim_match);
priv->clone = new_clone;
+
+ pipapo_gc_queue(set);
}
static bool nft_pipapo_transaction_mutex_held(const struct nft_set *set)
@@ -2192,6 +2224,7 @@ static int nft_pipapo_init(const struct nft_set *set,
priv->dirty = false;
+ INIT_LIST_HEAD(&priv->gc_head);
rcu_assign_pointer(priv->match, m);
return 0;
@@ -2244,6 +2277,8 @@ static void nft_pipapo_destroy(const struct nft_ctx *ctx,
struct nft_pipapo_match *m;
int cpu;
+ WARN_ON_ONCE(!list_empty(&priv->gc_head));
+
m = rcu_dereference_protected(priv->match, true);
if (m) {
rcu_barrier();
diff --git a/net/netfilter/nft_set_pipapo.h b/net/netfilter/nft_set_pipapo.h
index 519a2e6dc206f..a99baaeb5d926 100644
--- a/net/netfilter/nft_set_pipapo.h
+++ b/net/netfilter/nft_set_pipapo.h
@@ -165,6 +165,7 @@ struct nft_pipapo_match {
* @width: Total bytes to be matched for one packet, including padding
* @dirty: Working copy has pending insertions or deletions
* @last_gc: Timestamp of last garbage collection run, jiffies
+ * @gc_head: list of nft_trans_gc to queue up for mem reclaim
*/
struct nft_pipapo {
struct nft_pipapo_match __rcu *match;
@@ -172,6 +173,7 @@ struct nft_pipapo {
int width;
bool dirty;
unsigned long last_gc;
+ struct list_head gc_head;
};
struct nft_pipapo_elem;
--
2.43.0
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