netdev - Re: [PATCH net v2] net, sunrpc: Remap EPERM in case of connection failure in xs_tcp_setup

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Date: Mon, 1 Jul 2024 11:57:42 +0100
From: Simon Horman <horms@...nel.org>
To: Chuck Lever <chuck.lever@...cle.com>
Cc: Daniel Borkmann <daniel@...earbox.net>, kuba@...nel.org, neilb@...e.de,
	jlayton@...nel.org, kolga@...app.com, Dai.Ngo@...cle.com,
	tom@...pey.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
	Lex Siegel <usiegl00@...il.com>
Subject: Re: [PATCH net v2] net, sunrpc: Remap EPERM in case of connection
 failure in xs_tcp_setup_socket

On Fri, Jun 28, 2024 at 01:19:49PM -0400, Chuck Lever wrote:
> On Fri, Jun 28, 2024 at 06:31:23PM +0200, Daniel Borkmann wrote:
> > When using a BPF program on kernel_connect(), the call can return -EPERM. This
> > causes xs_tcp_setup_socket() to loop forever, filling up the syslog and causing
> > the kernel to potentially freeze up.
> > 
> > Neil suggested:
> > 
> >   This will propagate -EPERM up into other layers which might not be ready
> >   to handle it. It might be safer to map EPERM to an error we would be more
> >   likely to expect from the network system - such as ECONNREFUSED or ENETDOWN.
> > 
> > ECONNREFUSED as error seems reasonable. For programs setting a different error
> > can be out of reach (see handling in 4fbac77d2d09) in particular on kernels
> > which do not have f10d05966196 ("bpf: Make BPF_PROG_RUN_ARRAY return -err
> > instead of allow boolean"), thus given that it is better to simply remap for
> > consistent behavior. UDP does handle EPERM in xs_udp_send_request().
> > 
> > Fixes: d74bad4e74ee ("bpf: Hooks for sys_connect")
> > Fixes: 4fbac77d2d09 ("bpf: Hooks for sys_bind")
> > Co-developed-by: Lex Siegel <usiegl00@...il.com>
> > Signed-off-by: Lex Siegel <usiegl00@...il.com>
> > Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> > Link: https://github.com/cilium/cilium/issues/33395
> > Link: https://lore.kernel.org/bpf/171374175513.12877.8993642908082014881@noble.neil.brown.name
> > ---
> >  [ Fixes tags are set to the orig connect commit so that stable team
> >    can pick this up. ]
> > 
> >  v1 -> v2:
> >    - Plain resend, adding more sunrpc folks to Cc
> > 
> >  net/sunrpc/xprtsock.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index dfc353eea8ed..0e1691316f42 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -2441,6 +2441,13 @@ static void xs_tcp_setup_socket(struct work_struct *work)
> >  		transport->srcport = 0;
> >  		status = -EAGAIN;
> >  		break;
> > +	case -EPERM:
> > +		/* Happens, for instance, if a BPF program is preventing
> > +		 * the connect. Remap the error so upper layers can better
> > +		 * deal with it.
> > +		 */
> > +		status = -ECONNREFUSED;
> > +		fallthrough;
> >  	case -EINVAL:
> >  		/* Happens, for instance, if the user specified a link
> >  		 * local IPv6 address without a scope-id.
> > -- 
> > 2.21.0
> > 
> 
> Hi Daniel -
> 
> I know this is not documented in MAINTAINERS, but changes to
> net/sunrpc/xprtsock.c go to Anna Schumaker and Trond Myklebust,
> cc: linux-nfs@...r.

Would it be possible to update MAINTAINERS accordingly?