Re: [PATCH] proc: allow killing processes via file descriptors

[Andy Lutomirski]

> On Nov 18, 2018, at 12:44 PM, Daniel Colascione <dan...@google.com> wrote:
> 

> 
> That is, I'm proposing an API that looks like this:
> 
> int process_kill(int procfs_dfd, int signo, const union sigval value)
> 
> If, later, process_kill were to *also* accept process-capability FDs,
> nothing would break.

Except that this makes it ambiguous to the caller as to whether their current 
creds are considered.  So it would need to be a different syscall or at least a 
flag.  Otherwise a lot of those nice theoretical properties go away.

> Yes, that's what I have in mind. A siginfo_t is small enough that we
> could just store it as a blob allocated off the procfs inode or
> something like that without bothering with a shmfs file. You'd be able
> to read(2) the exit status as many times as you wanted.

I think that, if the syscall in question is read(2), then it should work *once* 
per struct file.  Otherwise running cat on the file would behave very oddly.

Read and poll have the same problem as write: we can’t check caps in read or 
poll either.