io_uring/poll: don't reissue in case of poll race on multishot request

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: io_uring/poll: don't reissue in case of poll race on multishot request A previous commit fixed a poll race that can occur, but it's only applicable for multishot requests. For a multishot request, we can safely ignore a spurious wakeup, as we never leave the waitqueue to begin with. A blunt reissue of a multishot armed request can cause us to leak a buffer, if they are ring provided. While this seems like a bug in itself, it's not really defined behavior to reissue a multishot request directly. It's less efficient to do so as well, and not required to rearm anything like it is for singleshot poll requests.

References

• https://git.kernel.org/stable/c/36fc7317cdb16cfeae0f879916995037bb615ac4
• https://git.kernel.org/stable/c/8caa03f10bf92cb8657408a6ece6a8a73f96ce13