In the Linux kernel, the following vulnerability has been resolved:

keys: Pin request_key_auth payload in instantiate paths

A: request_key()       B: KEYCTL_INSTANTIATE_IOV
================       =========================

create auth key
store rka in auth key
wait for helper
                       get auth key
                       load rka from auth key
                       copy user payload
                       sleep on #PF

helper completed
detach and free rka
destroy auth key
                       wake up
                       use rka->target_key
                       **USE-AFTER-FREE**

Give request_key_auth payloads a refcount.  Take a payload reference while
authkey->sem stabilizes the payload and revocation state.  Hold that
reference across the instantiate and reject paths.  Drop the auth key
owning reference from revoke and destroy.

[jarkko: Replaced the first two paragraphs of text with an actual
 concurrency scenario.]

https://git.kernel.org/stable/c/35ab4db86774d82389e4b9559e26ab7f68d8e395

https://git.kernel.org/stable/c/4982bfabce6b33b3c9eddb4fb900fe5568b7cf91

https://git.kernel.org/stable/c/708709c65a1832a99b0eef8ae46e343ddaca3d06

https://git.kernel.org/stable/c/7216ce8cb12fee44e309503955bb83806b106129

https://git.kernel.org/stable/c/83c0a1cb296d955d5f4d1f0bd8a769ba8ed8c29f

https://git.kernel.org/stable/c/d8274181b0f28d450b42489723a5ba81042158d7

https://git.kernel.org/stable/c/f9b68632ac93cc742f2e411021c4dbfe452ea0c2

https://git.kernel.org/stable/c/fd15b457a86939c38aa12116adabd8ff686c5e51

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