Subject: Re: [PATCH v3 8/9] io_uring/cmd: BPF hook for getsockopt cmd

From: Breno Leitao <[email-masked]>
Date: Mon, 21 Aug 2023 02:14:55 -0700

On Thu, Aug 17, 2023 at 03:08:47PM -0400, Gabriel Krisman Bertazi wrote:
> Breno Leitao <[email-masked]> writes:
> 
> > Add BPF hook support for getsockopts io_uring command. So, BPF cgroups
> > programs can run when SOCKET_URING_OP_GETSOCKOPT command is executed
> > through io_uring.
> >
> > This implementation follows a similar approach to what
> > __sys_getsockopt() does, but, using USER_SOCKPTR() for optval instead of
> > kernel pointer.
> >
> > Signed-off-by: Breno Leitao <[email-masked]>
> > ---
> >  io_uring/uring_cmd.c | 18 +++++++++++++-----
> >  1 file changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> > index a567dd32df00..9e08a14760c3 100644
> > --- a/io_uring/uring_cmd.c
> > +++ b/io_uring/uring_cmd.c
> > @@ -5,6 +5,8 @@
> >  #include <linux/io_uring.h>
> >  #include <linux/security.h>
> >  #include <linux/nospec.h>
> > +#include <linux/compat.h>
> > +#include <linux/bpf-cgroup.h>
> >  
> >  #include <uapi/linux/io_uring.h>
> >  #include <uapi/asm-generic/ioctls.h>
> > @@ -184,17 +186,23 @@ static inline int io_uring_cmd_getsockopt(struct socket *sock,
> >  	if (err)
> >  		return err;
> >  
> > -	if (level == SOL_SOCKET) {
> > +	err = -EOPNOTSUPP;
> > +	if (level == SOL_SOCKET)
> >  		err = sk_getsockopt(sock->sk, level, optname,
> >  				    USER_SOCKPTR(optval),
> >  				    KERNEL_SOCKPTR(&optlen));
> > -		if (err)
> > -			return err;
> >  
> > +	if (!(issue_flags & IO_URING_F_COMPAT))
> > +		err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level,
> > +						     optname,
> > +						     USER_SOCKPTR(optval),
> > +						     KERNEL_SOCKPTR(&optlen),
> > +						     optlen, err);
> > +
> > +	if (!err)
> >  		return optlen;
> > -	}
> 
> Shouldn't you call sock->ops->getsockopt for level!=SOL_SOCKET prior to
> running the hook?
> Before this patch, it would bail out with EOPNOTSUPP,
> but now the bpf hook gets called even for level!=SOL_SOCKET, which
> doesn't fit __sys_getsockopt. Am I misreading the code?

Not really, sock->ops->getsockopt() does not suport sockptr_t, but
__user addresses, differently from setsockopt()

          int             (*setsockopt)(struct socket *sock, int level,
                                        int optname, sockptr_t optval,
                                        unsigned int optlen);
          int             (*getsockopt)(struct socket *sock, int level,
                                        int optname, char __user *optval, int __user *optlen);

In order to be able to call sock->ops->getsockopt(), the callback
function will need to accepted sockptr.