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

[Martin KaFai Lau]

On 8/17/23 12:08 PM, Gabriel Krisman Bertazi wrote:
> Breno Leitao <leitao@xxxxxxxxxx> 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 <leitao@xxxxxxxxxx>
> > ---
> >   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?
I agree it should not call into bpf if the io_uring cannot support non 
SOL_SOCKET optnames. Otherwise, the bpf prog will get different optval and 
optlen when running in _sys_getsockopt vs io_uring getsockopt (e.g. in regular 
_sys_getsockopt(SOL_TCP), bpf expects the optval returned from tcp_getsockopt).

I think __sys_getsockopt can also be refactored similar to __sys_setsockopt in 
patch 3. Yes, for non SOL_SOCKET it only supports __user *optval and __user 
*optlen but may be a WARN_ON_ONCE/BUG_ON(sockpt_is_kernel(optval)) can be added 
before calling ops->getsockopt()? Then this details can be hidden away from the 
io_uring.