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([2001:41d0:303:db6b::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a35a06da5fsm3299225e9.3.2026.10.23.12.53.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Oct 2026 12:53:24 -0700 (PDT) From: Tristan Madani To: Steffen Klassert , Herbert Xu , "David S . Miller" Cc: Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Tristan Madani Subject: [PATCH ipsec] xfrm: fix output state cache TOCTOU in xfrm_state_find() Date: Fri, 23 Oct 2026 19:53:23 +0000 Message-ID: <20261023195323.3528192-1-tristmd@gmail.com> X-Mailer: git-send-email 2.47.3 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tristan Madani xfrm_state_find() checks x->km.state outside the xfrm_state_lock before inserting the state into the policy output state cache. Between the check and the lock acquisition, __xfrm_state_delete() can transition the state to XFRM_STATE_DEAD. The dead state is then inserted into the cache because the stale validity result is trusted after the lock is acquired. A subsequent call traversing the cache can then access a freed state, since xfrm_state_gc_destroy() does not unlink from state_cache_list. This is the output state cache counterpart of the input cache race fixed by commit ddd3d01329203 ("xfrm: Fix xfrm state cache insertion race"). Apply the same pattern: move the km.state validity check inside the lock so the check and the insertion are atomic with respect to __xfrm_state_delete(). Fixes: 0045e3d80613 ("xfrm: Cache used outbound xfrm states at the policy.") Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani --- net/xfrm/xfrm_state.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index e45aa1ed5b965..03baa50f0df7c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -1632,10 +1632,11 @@ xfrm_state_find(const xfrm_address_t *daddr, const xfrm_address_t *saddr, *err = acquire_in_progress ? -EAGAIN : error; } - if (x && x->km.state == XFRM_STATE_VALID && !cached && + if (x && !cached && (!(pol->flags & XFRM_POLICY_CPU_ACQUIRE) || x->pcpu_num == pcpu_id)) { spin_lock_bh(&net->xfrm.xfrm_state_lock); - if (hlist_unhashed(&x->state_cache)) + if (x->km.state == XFRM_STATE_VALID && + hlist_unhashed(&x->state_cache)) hlist_add_head_rcu(&x->state_cache, &pol->state_cache_list); spin_unlock_bh(&net->xfrm.xfrm_state_lock); } -- 2.47.3