linux-kernel - Re: [PATCH net 1/2] net: stmmac: est: Fix GCL bounds checks

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Message-ID: <2d00df77-870d-426c-a823-3a9f53d9eb30@altera.com>
Date: Thu, 11 Sep 2025 18:12:16 +0530
From: "G Thomas, Rohan" <rohan.g.thomas@...era.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jose Abreu <Jose.Abreu@...opsys.com>,
 Rohan G Thomas <rohan.g.thomas@...el.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Matthew Gerlach <matthew.gerlach@...era.com>
Subject: Re: [PATCH net 1/2] net: stmmac: est: Fix GCL bounds checks

Hi Russell,

Thanks for reviewing the patch.

On 9/11/2025 4:54 PM, Russell King (Oracle) wrote:
> On Thu, Sep 11, 2025 at 04:22:59PM +0800, Rohan G Thomas via B4 Relay wrote:
>> @@ -1012,7 +1012,7 @@ static int tc_taprio_configure(struct stmmac_priv *priv,
>>   		s64 delta_ns = qopt->entries[i].interval;
>>   		u32 gates = qopt->entries[i].gate_mask;
>>   
>> -		if (delta_ns > GENMASK(wid, 0))
>> +		if (delta_ns >= BIT(wid))
> 
> While I agree this makes it look better, you don't change the version
> below, which makes the code inconsistent. I also don't see anything
> wrong with the original comparison.

Just to clarify the intent behind this change:
For example, if wid = 3, then GENMASK(3, 0) = 0b1111 = 15. But the
maximum supported gate interval in this case is actually 7, since only 3
bits are available to represent the value. So in the patch, the
condition delta_ns >= BIT(wid) effectively checks if delta_ns is 8 or
more, which correctly returns an error for values that exceed the 3-bit
limit.

> Best Regards,
Rohan