linux-kernel - Re: [PATCH net 0/4] net: qede: avoid overruling error codes

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Message-ID: <ab165657-2c69-4b30-a371-6ad7fd28c539@fiberby.net>
Date: Sat, 27 Apr 2024 12:58:38 +0000
From: Asbjørn Sloth Tønnesen <ast@...erby.net>
To: Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Ariel Elior <aelior@...vell.com>, Manish Chopra <manishc@...vell.com>,
 Jiri Pirko <jiri@...nulli.us>, Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: [PATCH net 0/4] net: qede: avoid overruling error codes

Hi Simon,

Thank you for your review effort.

On 4/27/24 11:48 AM, Simon Horman wrote:
> On Fri, Apr 26, 2024 at 09:12:22AM +0000, Asbjørn Sloth Tønnesen wrote:
>> This series fixes the qede driver, so that
>> qede_parse_flow_attr() and it's subfunctions
>> doesn't get their error codes overruled
>> (ie. turning -EOPNOTSUPP into -EINVAL).
>>
>> ---
>> I have two more patches along the same lines,
>> but they are not yet causing any issues,
>> so I have them destined for net-next.
>> (those are for qede_flow_spec_validate_unused()
>> and qede_flow_parse_ports().)
>>
>> After that I have a series for converting to
>> extack + the final one for validating control
>> flags.
> 
> Hi,
> 
> I'm fine with these patches so far as the code changes go.
> But it is not clear to me that they are fixing a bug.
> 
> If so, I think some explanation should go in the commit messages.
> If not, I think these should be targeted at net-next
> (and not have Fixes tags.

Since I don't have the hardware I didn't try to construct commands, showing
the wrong error code being returned. I could make up some hypothetical commands,
and simulate how they would error. I assumed that the bug, was clear based on
the list of possible return values for each function.

As an example, in qede_parse_flow_attr() it validates dissector->used_keys,
and if an unsupported FLOW_DISSECTOR_KEY_* is set, then ede_parse_flow_attr()
returns -EOPNOTSUPP, which is returned to qede_add_tc_flower_fltr(),
and only check for non-zero, and since -EOPNOTSUPP is non zero,
then it returns -EINVAL. So if you try to match on a vlan tag,
then FLOW_DISSECTOR_KEY_VLAN would be set, and cause a -EOPNOTSUPP
to be returned, which then gets converted into a -EINVAL.

All drivers generally returns -EOPNOTSUPP in their used_keys checks, and
this driver clearly intended to do that as well.

The -EINVAL override was introduced in the same commit as the above check,
so it was broken from the start.

Another example is 319a1d19471e (blamed in 4th patch), Jiri added
a call to flow_action_basic_hw_stats_types_check() across multiple drivers,
and since -EINVAL was returned only a few lines above, then he assumed
that he could just return -EOPNOTSUPP, but that return value gets overruled
into a -EINVAL. It is clear from the commit that Jiri intended to return
-EOPNOTSUPP, but this part of the driver didn't follow the principle of
least astonishment, so that function could only fail with -EINVAL.

I think it's a bug, when another error code is returned than the one that
was clearly intended, but it's properly a low impact one.

> Also, if you do end posting a v2, blamed, is misspelt several
> times in commit messages.

Sorry about that, will fix that if a v2 turns out to be needed.

-- 
Best regards
Asbjørn Sloth Tønnesen
Network Engineer
Fiberby - AS42541