xfrm: policy: fix use-after-free on inexact bin in xfrm_policy_bysel_ctx()

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Fix the race by pruning the bin while still holding xfrm_policy_lock,
before dropping it. Use __xfrm_policy_inexact_prune_bin() directly since
the lock is already held. The wrapper xfrm_policy_inexact_prune_bin()
becomes unused and is removed.

Race:

  CPU0 (XFRM_MSG_DELPOLICY)           CPU1 (XFRM_MSG_NEWSPDINFO)
  ==========================          ==========================
  xfrm_policy_bysel_ctx():
    spin_lock_bh(xfrm_policy_lock)
    bin = xfrm_policy_inexact_lookup()
    __xfrm_policy_unlink(pol)
    spin_unlock_bh(xfrm_policy_lock)
    xfrm_policy_kill(ret)
    // wide window, lock not held
                                       xfrm_hash_rebuild():
                                         spin_lock_bh(xfrm_policy_lock)
                                         __xfrm_policy_inexact_flush():
                                           kfree_rcu(bin)  // bin freed
                                         spin_unlock_bh(xfrm_policy_lock)
    xfrm_policy_inexact_prune_bin(bin)
    // UAF: bin is freed

Fixes: 6be3b0db6d ("xfrm: policy: add inexact policy search tree infrastructure")
Signed-off-by: Sanghyun Park <sanghyun.park.cnu@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

...

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Sanghyun Park 2026-06-02 18:49:05 +09:00 • committed by Steffen Klassert

parent eb48730bb8

commit 7f2d76c9c0

1 changed files with 2 additions and 11 deletions

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net/xfrm/xfrm_policy.c

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