From 9fa903b24b1f46b4ff5443bcd4aca23e5c57f9c1 Mon Sep 17 00:00:00 2001 From: "Cen Zhang (Microsoft Security FORGE Labs)" Date: Wed, 26 Aug 2026 16:17:45 -0400 Subject: [PATCH] xfrm: hold net_device reference under RCU in bundle creation 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 this by reading dst->dev via dst_dev_rcu() and keeping the RCU read-side critical section active until xfrm_fill_dst() has taken the required device references. Fixes: 25ee3286dcbc ("[IPSEC]: Merge common code into xfrm_bundle_create") Fixes: a0073fe18e71 ("xfrm: Add a state resolution packet queue") Suggested-by: Steffen Klassert Reported-by: Xiang Mei (Microsoft) Link: https://lore.kernel.org/all/20260820200245.44312-1-blbllhy@gmail.com/ Cc: AutonomousCodeSecurity@microsoft.com Assisted-by: GitHub-Copilot:claude-opus-4.6 Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) Signed-off-by: Steffen Klassert --- net/xfrm/xfrm_policy.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c index 932a313b9460..513c9f228334 100644 --- a/net/xfrm/xfrm_policy.c +++ b/net/xfrm/xfrm_policy.c @@ -2770,9 +2770,12 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy, xdst0->path = dst; err = -ENODEV; - dev = dst->dev; - if (!dev) + rcu_read_lock(); + dev = dst_dev_rcu(dst); + if (!dev) { + rcu_read_unlock(); goto free_dst; + } xfrm_init_path(xdst0, dst, nfheader_len); xfrm_init_pmtu(bundle, nx); @@ -2780,8 +2783,10 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy, for (xdst_prev = xdst0; xdst_prev != (struct xfrm_dst *)dst; xdst_prev = (struct xfrm_dst *) xfrm_dst_child(&xdst_prev->u.dst)) { err = xfrm_fill_dst(xdst_prev, dev, fl); - if (err) + if (err) { + rcu_read_unlock(); goto free_dst; + } xdst_prev->u.dst.header_len = header_len; xdst_prev->u.dst.trailer_len = trailer_len; @@ -2789,6 +2794,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy, trailer_len -= xdst_prev->u.dst.xfrm->props.trailer_len; } + rcu_read_unlock(); return &xdst0->u.dst; put_states: @@ -3058,11 +3064,15 @@ 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; - if (!dev) + rcu_read_lock(); + dev = dst_dev_rcu(dst); + if (!dev) { + rcu_read_unlock(); goto free_dst; + } err = xfrm_fill_dst(xdst, dev, fl); + rcu_read_unlock(); if (err) goto free_dst;