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

Chuck Lever III
2024-07-01T14:04:49Z

> On Jul 1, 2024, at 6:57 AM, Simon Horman <horms@kernel.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@gmail.com>
>>> Signed-off-by: Lex Siegel <usiegl00@gmail.com>
>>> Signed-off-by: Daniel Borkmann <daniel@iogearbox.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@vger.
>
> 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