linux-kernel - Re: [PATCH v1 0/9] Fixes multiple sysctl bound checks

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Message-ID: <3b7a4fb3-9c88-47ca-afc3-a1bb7913fc3d@clip-os.org>
Date: Tue, 28 Jan 2025 10:43:13 +0100
From: Nicolas Bouchinet <nicolas.bouchinet@...p-os.org>
To: Joe Damato <jdamato@...tly.com>, linux-kernel@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-scsi@...r.kernel.org,
 codalist@...a.cs.cmu.edu, linux-nfs@...r.kernel.org, netdev@...r.kernel.org,
 netfilter-devel@...r.kernel.org, coreteam@...filter.org,
 Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>,
 Joel Granados <j.granados@...sung.com>, Bart Van Assche
 <bvanassche@....org>, Leon Romanovsky <leon@...nel.org>,
 Zhu Yanjun <yanjun.zhu@...ux.dev>, Jason Gunthorpe <jgg@...pe.ca>,
 Al Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v1 0/9] Fixes multiple sysctl bound checks

Hi,

Thank's for your reply.

On 1/27/25 19:05, Joe Damato wrote:
> On Mon, Jan 27, 2025 at 03:19:57PM +0100, nicolas.bouchinet@...p-os.org wrote:
>> From: Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>
>>
>> Hi,
>>
>> This patchset adds some bound checks to sysctls to avoid negative
>> value writes.
>>
>> The patched sysctls were storing the result of the proc_dointvec
>> proc_handler into an unsigned int data. proc_dointvec being able to
>> parse negative value, and it return value being a signed int, this could
>> lead to undefined behaviors.
>> This has led to kernel crash in the past as described in commit
>> 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
>>
>> Most of them are now bounded between SYSCTL_ZERO and SYSCTL_INT_MAX.
>> nf_conntrack_expect_max is bounded between SYSCTL_ONE and SYSCTL_INT_MAX
>> as defined by its documentation.
> I noticed that none of the patches have a Fixes tags. Do any of
> these fix existing crashes or is this just cleanup?

I've just saw that xfrm{4,6}_gc_thresh sysctls where obsolete since 4.14 
in the documentation...

Also, ipv4_dst_ops.gc_thresh is set to `~0` since commit 4ff3885262d0 
("ipv4: Delete routing cache.").

Wich will be printed as -1 when this syctl is read.

```
$ cat /proc/sys/net/ipv4/route/gc_thresh
-1
```

IIUC, it seems to be used in order to disable the garbage collection, 
hence, this patch would make it impossible
to a user to disable it this way.
It should thus be bounded it between SYSCTL_NEG_ONE and SYSCTL_INT_MAX.


Your right, it's only cleanup, I'll push patch 3 separately only on 
netdev, with extended impact analyses, sorry for that.


>
> I am asking because if this is cleanup then it would be "net-next"
> material instead of "net" and would need to be resubmit when then
> merge window has passed [1].
>
> FWIW, I submit a similar change some time ago and it was submit to
> net-next as cleanup [2].
>
> [1]: https://lore.kernel.org/netdev/20250117182059.7ce1196f@kernel.org/
> [2]: https://lore.kernel.org/netdev/CANn89i+=HiffVo9iv2NKMC2LFT15xFLG16h7wN3MCrTiKT3zQQ@mail.gmail.com/T/
>