linux-kernel - Re: [PATCH net v3] ptp: Add a upper bound on max

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Message-ID: <20250926153021.46848cca@kernel.org>
Date: Fri, 26 Sep 2025 15:30:21 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: I Viswanath <viswanathiyyappan@...il.com>
Cc: richardcochran@...il.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, pabeni@...hat.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
 linux-kernel-mentees@...ts.linux.dev, david.hunter.linux@...il.com,
 syzbot+94d20db923b9f51be0df@...kaller.appspotmail.com
Subject: Re: [PATCH net v3] ptp: Add a upper bound on max_vclocks

On Thu, 25 Sep 2025 21:29:08 +0530 I Viswanath wrote:
> This can be reproduced by executing: 
> 
> echo x > /sys/devices/virtual/ptp/ptp0/max_vclocks
> 
> where x > KMALLOC_MAX_SIZE/(sizeof(int)) which computes to 1048576 on
> my system
> 
> What would be a reasonable value for PTP_MAX_VCLOCKS_LIMIT?

I wonder about that, too. Perhaps tying uAPI behavior to
KMALLOC_MAX_SIZE is going to come back to bite us. But I don't
have a great idea for what the max should be.

> KMALLOC_MAX_SIZE/(sizeof(int)) is the absolute max value for which the 
> memory allocation won't fail