Hello.
There is a discrepancy between the man page description of
'SO_PEERCRED' and real behavior.
`man 7 unix` states:
```
SO_PEERCRED
This read-only socket option returns the credentials of
the peer process connected to this socket. The returned
credentials are those that were in effect at the time of
the call to connect(2) or socketpair(2).
```
This doesn't match real behavior in following situation (just an example):
- process starts with uid=0, gid=0
- process creates UNIX socket, binds it, listens on it
- process changes to uid=uid1, git=gid1 (using `setresuid()`, `setresgid()`)
- another process connects to the listening socket and requests
peer's credentials using `getsockopt(... SOL_SOCKET, SO_PEERCRED ...)`
According to the man page: SO_PEERCRED should report (uid1, gid1),
because peer process was running under (uid1, gid1) "at the time of
the call to connect(2)"
In reality SO_PEERCRED reports (0, 0)
Reproducing code is available in
https://bugzilla.redhat.com/show_bug.cgi?id=2247682
I'm not entirely sure if this is a real bug or rather a poor
description in the man page, but I tend to think that it's the latter.
