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

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Date: Mon, 21 Aug 2023 13:03:08 -0400
From: Gabriel Krisman Bertazi <krisman@...e.de>
To: Breno Leitao <leitao@...ian.org>
Cc: sdf@...gle.com,  axboe@...nel.dk,  asml.silence@...il.com,
  willemdebruijn.kernel@...il.com,  martin.lau@...ux.dev,
  bpf@...r.kernel.org,  linux-kernel@...r.kernel.org,
  netdev@...r.kernel.org,  io-uring@...r.kernel.org,  kuba@...nel.org,
  pabeni@...hat.com
Subject: Re: [PATCH v3 8/9] io_uring/cmd: BPF hook for getsockopt cmd

Breno Leitao <leitao@...ian.org> writes:

> On Thu, Aug 17, 2023 at 03:08:47PM -0400, Gabriel Krisman Bertazi wrote:
>> Breno Leitao <leitao@...ian.org> 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@...ian.org>
>> > ---
>> >  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.

So, it seems you won't support !SOL_SOCKETs here.  Then, I think you
shouldn't call the hook for those sockets. My main concern is that we
remain compatible to __sys_getsockopt when invoking the hook.

I think you should just have the following as the very first thing in
the function (but after the security_ check).

if (level != SOL_SOCKET)
   return -EOPNOTSUPP;

-- 
Gabriel Krisman Bertazi