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Date:   Tue, 6 Dec 2022 15:37:05 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Ryder Lee <Ryder.Lee@mediatek.com>
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Subject: Re: Coverity: mt7996_hw_queue_read(): Integer handling issues
Message-ID: <202212061535.5D3DA489FB@keescook>
References: <202212021411.A5E618D3@keescook>
 <786eff1a1751a5bc0dc68d6567be585b635bddb1.camel@mediatek.com>
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On Sat, Dec 03, 2022 at 04:40:09AM +0000, Ryder Lee wrote:
> On Fri, 2022-12-02 at 14:11 -0800, coverity-bot wrote:
> > Hello!
> > 
> > This is an experimental semi-automated report about issues detected
> > by
> > Coverity from a scan of next-20221202 as part of the linux-next scan
> > project:
> > 
> https://urldefense.com/v3/__https://scan.coverity.com/projects/linux-next-weekly-scan__;!!CTRNKA9wMg0ARbw!jBOoj6LMqqA8E0AyjKQTa-0rVzcFiZ3BbpciEIn7so974kcMBeG4zZm-QU4AudLXY7-jNUSt0unzAt2zirSF$?
> >  
> > 
> > You're getting this email because you were associated with the
> > identified
> > lines of code (noted below) that were touched by commits:
> > 
> >   Thu Dec 1 17:29:14 2022 +0100
> >     98686cd21624 ("wifi: mt76: mt7996: add driver for MediaTek Wi-Fi
> > 7 (802.11be) devices")
> > 
> > Coverity reported the following:
> > 
> > *** CID 1527813:  Integer handling issues  (SIGN_EXTENSION)
> > drivers/net/wireless/mediatek/mt76/mt7996/debugfs.c:460 in
> > mt7996_hw_queue_read()
> > 454     	for (i = 0; i < size; i++) {
> > 455     		u32 ctrl, head, tail, queued;
> > 456
> > 457     		if (val & BIT(map[i].index))
> > 458     			continue;
> > 459
> > vvv     CID 1527813:  Integer handling issues  (SIGN_EXTENSION)
> > vvv     Suspicious implicit sign extension: "map[i].qid" with type
> > "u8" (8 bits, unsigned) is promoted in "map[i].qid << 24" to type
> > "int" (32 bits, signed), then sign-extended to type "unsigned long"
> > (64 bits, unsigned).  If "map[i].qid << 24" is greater than
> > 0x7FFFFFFF, the upper bits of the result will all be 1.
> > 460     		ctrl = BIT(31) | (map[i].pid << 10) |
> > (map[i].qid << 24);
> 
> u32 ctrl = BIT(31) | (map[i].pid << 10) | (map[i].qid << 24);
> 
> Hmm ...where's type "int" (32 bits, signed) from?

	map[i].qid is promoted to int before the "<< 24".

-- 
Kees Cook