Messages in this thread | | | From | Linus Torvalds <> | Date | Sat, 20 Mar 2021 10:56:36 -0700 | Subject | Re: [PATCH 1/2] signal: don't allow sending any signals to PF_IO_WORKER threads |
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On Sat, Mar 20, 2021 at 9:19 AM Eric W. Biederman <ebiederm@xmission.com> wrote: > > The creds should be reasonably in-sync with the rest of the threads.
It's not about credentials (despite the -EPERM).
It's about the fact that kernel threads cannot handle signals, and then get caught in endless loops of "if (sigpending()) return -EAGAIN".
For a normal user thread, that "return -EAGAIN" (or whatever) will end up returning an error to user space - and before it does that, it will go through the "oh, returning to user space, so handle signal" path. Which will clear sigpending etc.
A thread that never returns to user space fundamentally cannot handle this. The sigpending() stays on forever, the signal never gets handled, the thread can't do anything.
So delivering a signal to a kernel thread fundamentally cannot work (although we do have some threads that explicitly see "oh, if I was killed, I will exit" - think things like in-kernel nfsd etc).
Linus
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