Re: [PATCH mptcp-net 0/9] net: sysctl: avoid using current->nsproxy

[Matthieu Baerts <matttbe@kernel.org>]

Hi Mat,

On 08/01/2025 02:49, Mat Martineau wrote:
> On Tue, 7 Jan 2025, Matthieu Baerts (NGI0) wrote:
> 
>> As pointed out by Al Viro and Eric Dumazet in [1], using the 'net'
>> structure via 'current' is not recommended for different reasons:
>>
>> - Inconsistency: getting info from the reader's/writer's netns vs only
>>  from the opener's netns.
>>
>> - current->nsproxy can be NULL in some cases, resulting in an 'Oops'
>>  (null-ptr-deref), e.g. when the current task is exiting, as spotted by
>>  syzbot [1] using acct(2).
>>
>> The 'net' or 'pernet' structure can be obtained from the table->data
>> using container_of().
>>
>> Note that table->data could also be used directly in more places, but
>> that would increase the size of this fix to replace all accesses via
>> 'net'.
>>
>> Patches 2-9 remove access of net via current->nsproxy in sysfs handlers
>> in MPTCP, SCTP and RDS. There are multiple patches to ease the
>> backports.
>>
>> Patch 1 is not directly linked to this, but it is a small fix for MPTCP
>> available_schedulers sysctl knob to explicitly mark it as read-only.
>>
>> Please note that this series does not address Al's comment [2]. In SCTP,
>> some sysctl knobs set other sysfs-exposed variables for the min/max: two
>> processes could then write two linked values at the same time, resulting
>> in new values being outside the new boundaries.
> 
> 
> Thanks Matthieu,
> 
> The mptcp patches (1-3) LGTM:
> 
> Reviewed-by: Mat Martineau <martineau@kernel.org>
> 
> 
> The sctp and rds patches look fine as well.

Thank you for this review!

Patches are now in our tree (fixes for -net) with your RvB tag on the 3
first ones. I will upstream them later on today.

New patches for t/upstream-net and t/upstream:
- 968e9bb5a4cd: mptcp: sysctl: avail sched: remove write access
- eda363130f80: mptcp: sysctl: sched: avoid using current->nsproxy
- c838529f87ee: mptcp: sysctl: blackhole timeout: avoid using
current->nsproxy
- fb1a7a8fb16c: sctp: sysctl: cookie_hmac_alg: avoid using current->nsproxy
- a18c9552dca0: sctp: sysctl: rto_min/max: avoid using current->nsproxy
- 8408f9182e52: sctp: sysctl: auth_enable: avoid using current->nsproxy
- c45cb99c9aa0: sctp: sysctl: udp_port: avoid using current->nsproxy
- 3df3f684ee7e: sctp: sysctl: plpmtud_probe_interval: avoid using
current->nsproxy
- a77b912deb35: rds: sysctl: rds_tcp_{rcv,snd}buf: avoid using
current->nsproxy
- Results: bd3d4b1ab1bc..d66993cd4a59 (export-net)
- Results: ebe8ebeee62e..f289bc80702c (export)

Tests are now in progress:

- export-net:
https://github.com/multipath-tcp/mptcp_net-next/commit/6c101bff7e1613c0087472d2ee78c986e221435e/checks
- export:
https://github.com/multipath-tcp/mptcp_net-next/commit/0e96d0da96b041f087c5c0b46bc34978572ccffe/checks

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.