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 14:04:22 +0000
From: Chuck Lever III <chuck.lever@...cle.com>
To: Simon Horman <horms@...nel.org>
CC: Daniel Borkmann <daniel@...earbox.net>, Jakub Kicinski <kuba@...nel.org>,
        Neil Brown <neilb@...e.de>, Jeff Layton <jlayton@...nel.org>,
        Olga
 Kornievskaia <kolga@...app.com>, Dai Ngo <dai.ngo@...cle.com>,
        Tom Talpey
	<tom@...pey.com>, netdev <netdev@...r.kernel.org>,
        "bpf@...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 Jul 1, 2024, at 6:57 AM, Simon Horman <horms@...nel.org> wrote:
> 
> 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?

I can do it, of course, but I'd like to discuss this
with the NFS client maintainers to ensure they agree
on how the files are divided between the trees.


--
Chuck Lever