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[45.78.65.84]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-13fab4f83c3sm3296821c88.14.2026.07.31.08.30.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Jul 2026 08:30:40 -0700 (PDT) From: Chengfeng Ye To: Jamal Hadi Salim , Jiri Pirko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Vlad Buslov , Stefano Brivio Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Chengfeng Ye , stable@vger.kernel.org Subject: [PATCH net] net/sched: keep tcf block alive during offload unbind Date: Fri, 31 Jul 2026 23:30:31 +0800 Message-ID: <20260731153031.3201165-1-nicoyip.dev@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit An RTNL-unlocked filter request can race with qdisc teardown on a shared tcf block. The filter request takes a temporary block reference before teardown drops the qdisc owner's reference. Teardown then enters tcf_block_offload_unbind() without retaining a reference of its own. The following interleaving can occur: filter request qdisc teardown tcf_block_refcnt_get(): 1 -> 2 __tcf_block_put(): 2 -> 1 tcf_block_offload_unbind() tcf_block_refcnt_put(): 1 -> 0 tcf_block_destroy() access block->nooffloaddevcnt The unbind path may sleep in flow_indr_dev_setup_offload(), allowing the RCU grace period to expire and the block to be reclaimed. It then continues using block->cb_lock and block->nooffloaddevcnt. KASAN reported: BUG: KASAN: slab-use-after-free in tcf_block_offload_unbind Read of size 4 at addr ffff88811ae590a4 Call Trace: tcf_block_offload_unbind+0x158/0x190 clsact_destroy+0xd6/0x690 __qdisc_destroy+0xdf/0x290 qdisc_graft+0x5d7/0x1560 tc_get_qdisc+0x415/0xd50 rtnetlink_rcv_msg+0x367/0xa40 Allocated by task 85: tcf_block_get_ext+0x803/0x1570 clsact_init+0x1ff/0xb50 qdisc_create+0x392/0xde0 Freed by task 88: __kasan_slab_free+0x43/0x70 __rcu_free_sheaf_prepare+0x5c/0x220 rcu_free_sheaf+0x1a/0x100 Keep the qdisc owner's reference until offload unbind completes by moving the unbind before the refcount decrement. A concurrent temporary reference release can no longer destroy the block while unbind uses it. Fixes: 92149190067d ("net: sched: flower: set unlocked flag for flower proto ops") Cc: stable@vger.kernel.org Signed-off-by: Chengfeng Ye --- net/sched/cls_api.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c index fee4524adc98..d3b2506d87cf 100644 --- a/net/sched/cls_api.c +++ b/net/sched/cls_api.c @@ -1312,6 +1312,9 @@ static struct tcf_block *__tcf_block_find(struct net *net, struct Qdisc *q, static void __tcf_block_put(struct tcf_block *block, struct Qdisc *q, struct tcf_block_ext_info *ei, bool rtnl_held) { + if (q) + tcf_block_offload_unbind(block, q, ei); + if (refcount_dec_and_mutex_lock(&block->refcnt, &block->lock)) { /* Flushing/putting all chains will cause the block to be * deallocated when last chain is freed. However, if chain_list @@ -1325,15 +1328,10 @@ static void __tcf_block_put(struct tcf_block *block, struct Qdisc *q, if (tcf_block_shared(block)) tcf_block_remove(block, block->net); - if (q) - tcf_block_offload_unbind(block, q, ei); - if (free_block) tcf_block_destroy(block); else tcf_block_flush_all_chains(block, rtnl_held); - } else if (q) { - tcf_block_offload_unbind(block, q, ei); } } -- 2.43.0