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([2a0d:3344:5521:6b10:58fd:68f:7756:389d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f85bb5a46sm56558149f8f.9.2026.07.28.03.34.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jul 2026 03:34:34 -0700 (PDT) Message-ID: <3914dd5c-77c8-4f96-8bfc-986f0a00f722@redhat.com> Date: Tue, 28 Jul 2026 12:34:32 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 1/1] net/sched: cls_route: fix fastmap use-after-free on filter To: Jamal Hadi Salim , netdev@vger.kernel.org Cc: kuba@kernel.org, davem@davemloft.net, edumazet@google.com, horms@kernel.org, john.fastabend@gmail.com, jiri@resnulli.us, zdi-disclosures@trendmicro.com, sh.kalluri129@gmail.com, victor@mojatatu.com, security@kernel.org, stable@vger.kernel.org, Santosh Kalluri References: <20260723105210.817079-1-jhs@mojatatu.com> From: Paolo Abeni Content-Language: en-US In-Reply-To: <20260723105210.817079-1-jhs@mojatatu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/23/26 12:52 PM, Jamal Hadi Salim wrote: > diff --git a/net/sched/cls_route.c b/net/sched/cls_route.c > index bd6f945bd388..700f878fc3cd 100644 > --- a/net/sched/cls_route.c > +++ b/net/sched/cls_route.c > @@ -297,16 +297,29 @@ static void route4_destroy(struct tcf_proto *tp, bool rtnl_held, > next = rtnl_dereference(f->next); > RCU_INIT_POINTER(b->ht[h2], next); > tcf_unbind_filter(tp, &f->res); > - if (tcf_exts_get_net(&f->exts)) > - route4_queue_work(f); > - else > - __route4_delete_filter(f); > + /* Always defer the free. The direct > + * __route4_delete_filter() path has no > + * grace period and races with readers > + * that cached f in the fastmap. > + */ > + tcf_exts_get_net(&f->exts); > + route4_queue_work(f); Sashiko fears the above would be race prone: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260723105210.817079-1-jhs%40mojatatu.com > } > } > RCU_INIT_POINTER(head->table[h1], NULL); > kfree_rcu(b, rcu); > } > } > + > + /* All filters are unlinked; no new reader can find them on the > + * chain. Wait for in-flight readers that may still hold a filter > + * pointer and have published it into the fastmap after we unlinked. > + * Then flush the stale entries while head is still valid under > + * RTNL, matching the route4_delete() pattern. > + */ > + synchronize_rcu(); > + route4_reset_fastmap(head); This really looks like quite a big hammer. Since there is already a synchronization point for both reader and write while acquiring the fastmap_lock, I'm wondering if something alike the following could work ?!? (completely untested!!!): --- diff --git a/net/sched/cls_route.c b/net/sched/cls_route.c index bd6f945bd388..8cecc945dcde 100644 --- a/net/sched/cls_route.c +++ b/net/sched/cls_route.c @@ -52,6 +52,7 @@ struct route4_filter { struct tcf_result res; struct tcf_exts exts; u32 handle; + bool dying; struct route4_bucket *bkt; struct tcf_proto *tp; struct rcu_work rwork; @@ -66,9 +67,11 @@ static inline int route4_fastmap_hash(u32 id, int iif) static DEFINE_SPINLOCK(fastmap_lock); static void -route4_reset_fastmap(struct route4_head *head) +route4_reset_fastmap(struct route4_head *head, struct route4_filter *f) { spin_lock_bh(&fastmap_lock); + if (f) + f->dying = true; memset(head->fastmap, 0, sizeof(head->fastmap)); spin_unlock_bh(&fastmap_lock); } @@ -81,9 +84,11 @@ route4_set_fastmap(struct route4_head *head, u32 id, int iif, /* fastmap updates must look atomic to aling id, iff, filter */ spin_lock_bh(&fastmap_lock); - head->fastmap[h].id = id; - head->fastmap[h].iif = iif; - head->fastmap[h].filter = f; + if (!f->dying) { + head->fastmap[h].id = id; + head->fastmap[h].iif = iif; + head->fastmap[h].filter = f; + } spin_unlock_bh(&fastmap_lock); } @@ -338,7 +343,7 @@ static int route4_delete(struct tcf_proto *tp, void *arg, bool *last, * notice we unlink'd the filter so we can't get it * back in the fastmap. */ - route4_reset_fastmap(head); + route4_reset_fastmap(head, f); /* Delete it */ tcf_unbind_filter(tp, &f->res); @@ -558,7 +563,7 @@ static int route4_change(struct net *net, struct sk_buff *in_skb, } } - route4_reset_fastmap(head); + route4_reset_fastmap(head, fold); *arg = f; if (fold) { tcf_unbind_filter(tp, &fold->res);