Re: [Libguestfs] [PATCH nbdkit v2 1/3] server: Add new APIs for reading the client’s SO_PEERCRED.

On 10/3/20 1:50 PM, Richard W.M. Jones wrote: > New nbdkit_peer_pid, nbdkit_peer_uid and nbdkit_peer_gid calls can be > used on Linux (only) to read the peer PID, UID and GID from clients > connected over a Unix domain socket. This can be used in the > preconnect phase to add additional filtering. > > One use for this is to add an extra layer of authentication for local > connections. A subsequent commit will enhance the now misnamed > nbdkit-ip-filter to allow filtering on these extra fields. > > It appears as if it would be possible to implement this for FreeBSD > too (see comment in code). > --- > docs/nbdkit-plugin.pod | 47 +++++++++++++++-- > include/nbdkit-common.h | 3 ++ > server/nbdkit.syms | 3 ++ > server/public.c | 108 ++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 156 insertions(+), 5 deletions(-) > > +=head2 C<nbdkit_peer_pid> > + > +(nbdkit E<ge> 1.24) > + > + int nbdkit_peer_pid (void); > + > +Return the peer process ID. This is only available when the client > +connected over a Unix domain socket, and only works for Linux. > + > +On success this returns the peer process ID. On error, > +C<nbdkit_error> is called and this call returns C<-1>. Is int always going to be sufficient? Or are there platforms with 64-bit pid_t? Mingw is an interesting beast; I've seen conflicting stories on whether 64-bit windows has 32- or 64-bit pids (the spawn APIs manage 64-bit handles, but other windows APIs return 32-bit int), so 64-bit pid_t on mingw does seem to be a real concern. > + > +=head2 C<nbdkit_peer_uid> > + > +(nbdkit E<ge> 1.24) > + > + int nbdkit_peer_uid (void); > + > +Return the peer user ID. This is only available when the client > +connected over a Unix domain socket, and only works for Linux. > + > +On success this returns the user ID. On error, C<nbdkit_error> is > +called and this call returns C<-1>. > + > +=head2 C<nbdkit_peer_gid> > + > +(nbdkit E<ge> 1.24) > + > + int nbdkit_peer_gid (void); int for these two is probably fine. > + > +Return the peer group ID. This is only available when the client > +connected over a Unix domain socket, and only works for Linux. > + > +On success this returns the user ID. On error, C<nbdkit_error> is > +called and this call returns C<-1>. > + > =head1 DEBUGGING > > +static int > +get_peercred (int s, int *pid, int *uid, int *gid) > +{ > + struct ucred ucred; > + socklen_t n = sizeof ucred; > + > + if (getsockopt (s, SOL_SOCKET, SO_PEERCRED, &ucred, &n) == -1) { > + nbdkit_error ("getsockopt: SO_PEERCRED: %m"); > + return -1; > + } > + > + if (pid && ucred.pid >= 1) { > + if (ucred.pid <= INT_MAX) > + *pid = ucred.pid; > + else > + nbdkit_error ("pid out of range: cannot be mapped to int"); > + } well, at least you are acknowledging that int might not always map to pid_t. Otherwise, looks fine to me.