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Thu, 20 Aug 2026 13:02:53 -0700 (PDT) Received: from mac.lan ([136.55.173.105]) by smtp.gmail.com with ESMTPSA id 00721157ae682-84511abce11sm30016807b3.2.2026.08.20.13.02.52 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 20 Aug 2026 13:02:52 -0700 (PDT) From: "Cen Zhang (Microsoft)" To: steffen.klassert@secunet.com, herbert@gondor.apana.org.au, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com Cc: horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, xmei5@asu.edu, tgopinath@linux.microsoft.com, kys@microsoft.com, blbllhy@gmail.com Subject: [PATCH net] xfrm: hold net_device reference under RCU in bundle creation Date: Thu, 20 Aug 2026 16:02:45 -0400 Message-ID: <20260820200245.44312-1-blbllhy@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit xfrm_bundle_create() and xfrm_create_dummy_bundle() read dst->dev into a local pointer without taking a device reference, then pass it to xfrm_fill_dst(). A concurrent RTM_DELLINK replaces dst->dev via dst_dev_put() and frees the old net_device, causing a use-after-free when xfrm6_fill_dst() later dereferences the stale dev pointer. BUG: KASAN: slab-use-after-free in xfrm6_fill_dst+0x82c/0x860 (net/ipv6/xfrm6_policy.c:86 netdev_hold()) Read of size 8 at addr ffff8880142fe588 by task exploit/153 Call Trace: xfrm6_fill_dst+0x82c/0x860 xfrm_resolve_and_create_bundle+0x21d4/0x2bd0 xfrm_lookup_with_ifid+0x485/0x1640 ip6_dst_lookup_flow+0x19b/0x1e0 udpv6_sendmsg+0x1443/0x2dd0 Fix by reading dst->dev under rcu_read_lock() via dst_dev_rcu() and taking dev_hold() before leaving the RCU critical section. To properly release the reference, add dev_put() on both the success and error paths, and initialize dev to NULL to prevent dev_put() on an uninitialized pointer when put_states falls through to free_dst before dev is assigned. Fixes: 25ee3286dcbc ("[IPSEC]: Merge common code into xfrm_bundle_create") Fixes: a0073fe18e71 ("xfrm: Add a state resolution packet queue") Reported-by: AutonomousCodeSecurity@microsoft.com Reported-by: Xiang Mei (Microsoft) Reported-by: Cen Zhang (Microsoft) Signed-off-by: Cen Zhang (Microsoft) --- net/xfrm/xfrm_policy.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c index 932a313b9460..13585ff24aba 100644 --- a/net/xfrm/xfrm_policy.c +++ b/net/xfrm/xfrm_policy.c @@ -2668,7 +2668,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy, const struct xfrm_mode *inner_mode; struct net *net = xp_net(policy); unsigned long now = jiffies; - struct net_device *dev; + struct net_device *dev = NULL; struct xfrm_dst *xdst_prev = NULL; struct xfrm_dst *xdst0 = NULL; int i = 0; @@ -2770,7 +2770,11 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy, xdst0->path = dst; err = -ENODEV; - dev = dst->dev; + rcu_read_lock(); + dev = dst_dev_rcu(dst); + if (dev) + dev_hold(dev); + rcu_read_unlock(); if (!dev) goto free_dst; @@ -2789,6 +2793,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy, trailer_len -= xdst_prev->u.dst.xfrm->props.trailer_len; } + dev_put(dev); return &xdst0->u.dst; put_states: @@ -2798,6 +2803,8 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy, if (xdst0) dst_release_immediate(&xdst0->u.dst); + if (dev) + dev_put(dev); return ERR_PTR(err); } @@ -3058,11 +3065,16 @@ static struct xfrm_dst *xfrm_create_dummy_bundle(struct net *net, xfrm_init_path((struct xfrm_dst *)dst1, dst, 0); err = -ENODEV; - dev = dst->dev; + rcu_read_lock(); + dev = dst_dev_rcu(dst); + if (dev) + dev_hold(dev); + rcu_read_unlock(); if (!dev) goto free_dst; err = xfrm_fill_dst(xdst, dev, fl); + dev_put(dev); if (err) goto free_dst; -- 2.55.0