From ba4ba11ed6eb8972c69070417fc27b48deb002e8 Mon Sep 17 00:00:00 2001 From: Norbert Szetei Date: Sun, 6 Sep 2026 10:21:09 +0200 Subject: [PATCH] net: openvswitch: fix use-after-free of the flow table mask array tbl_mask_array_realloc() retires the old mask_array before it stops being reachable: old = ovsl_dereference(tbl->mask_array); if (old) { ... call_rcu(&old->rcu, mask_array_rcu_cb); } rcu_assign_pointer(tbl->mask_array, new); call_rcu() only waits for read-side critical sections already in flight. tbl->mask_array still points at old between the call_rcu() and the rcu_assign_pointer(), so a reader entering ovs_flow_tbl_lookup_stats() in that window picks up old in a fresh critical section that the pending grace period does not cover. tbl_mask_array_realloc() runs in process context under ovs_mutex, so the window is preemptible and can outlast the grace period. Then mask_array_rcu_cb() frees old before the swap runs: BUG: KASAN: slab-use-after-free in flow_lookup.constprop.0+0x2bf/0x2f0 Read of size 8 at addr ffff888020b3e018 by task poc/741 flow_lookup.constprop.0+0x2bf/0x2f0 ovs_flow_tbl_lookup_stats+0x4a3/0x5c0 ovs_dp_process_packet+0x19c/0x710 ovs_vport_receive+0x243/0x390 internal_dev_xmit+0x81/0x170 Freed by task 728: kfree+0x16a/0x4e0 rcu_core+0x853/0x1030 Publish the new array before retiring the old one. The kfree_rcu() that call_rcu() replaced ran after the swap. Fixes: eac87c413bf9 ("net: openvswitch: reorder masks array based on usage") Cc: stable@vger.kernel.org Signed-off-by: Norbert Szetei Reviewed-by: Ilya Maximets Acked-by: Eelco Chaudron echaudro@redhat.com Link: https://patch.msgid.link/DE115F9C-2545-423E-A702-986FC952FD62@doyensec.com Signed-off-by: Jakub Kicinski --- net/openvswitch/flow_table.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c index 67d5b8c0fe79..1e0f9d193eb0 100644 --- a/net/openvswitch/flow_table.c +++ b/net/openvswitch/flow_table.c @@ -257,11 +257,13 @@ static int tbl_mask_array_realloc(struct flow_table *tbl, int size) if (ovsl_dereference(old->masks[i])) new->masks[new->count++] = old->masks[i]; } - call_rcu(&old->rcu, mask_array_rcu_cb); } rcu_assign_pointer(tbl->mask_array, new); + if (old) + call_rcu(&old->rcu, mask_array_rcu_cb); + return 0; }