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 <steffen.klassert@secunet.com>
Reported-by: Xiang Mei (Microsoft) <xmei5@asu.edu>
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) <blbllhy@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

0 files changed, 0 insertions, 0 deletions