Re: Coverity: mt7915_mcu_get_chan_mib_info(): Memory - illegal accesses

From: Ryder Lee <Ryder.Lee@mediatek.com>
To: "keescook@chromium.org" <keescook@chromium.org>,
	"Bo Jiao (焦波)" <Bo.Jiao@mediatek.com>
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Subject: Re: Coverity: mt7915_mcu_get_chan_mib_info(): Memory - illegal accesses
Date: Fri, 2 Dec 2022 22:56:19 +0000	[thread overview]
Message-ID: <1a16599dd5e4eed86bae112a232a3599af43a5f2.camel@mediatek.com> (raw)
In-Reply-To: <202212021424.34C0F695E4@keescook>

On Fri, 2022-12-02 at 14:24 -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!j7j_C0KpO4VD2yMOodvpeIexTGq4fhy2yq6nokNua9u4LToiUOLk4ou8JFFNrXkrh80d5BK2k44faRQstHE9$ 
>  
> 
> You're getting this email because you were associated with the
> identified
> lines of code (noted below) that were touched by commits:
> 
>   Thu Feb 3 13:57:56 2022 +0100
>     417a4534d223 ("mt76: mt7915: update mt7915_chan_mib_offs for
> mt7916")
> 
> Coverity reported the following:
> 
> *** CID 1527801:  Memory - illegal accesses  (OVERRUN)
> drivers/net/wireless/mediatek/mt76/mt7915/mcu.c:3005 in
> mt7915_mcu_get_chan_mib_info()
> 2999     		start = 5;
> 3000     		ofs = 0;
> 3001     	}
> 3002
> 3003     	for (i = 0; i < 5; i++) {
> 3004     		req[i].band = cpu_to_le32(phy->mt76->band_idx);
> vvv     CID 1527801:  Memory - illegal accesses  (OVERRUN)
> vvv     Overrunning array "offs" of 9 4-byte elements at element
> index 9 (byte offset 39) using index "i + start" (which evaluates to
> 9).
> 3005     		req[i].offs = cpu_to_le32(offs[i + start]);
> 3006
> 3007     		if (!is_mt7915(&dev->mt76) && i == 3)
> 3008     			break;
> 3009     	}
> 3010
> 
> If this is a false positive, please let us know so we can mark it as
> such, or teach the Coverity rules to be smarter. If not, please make
> sure fixes get into linux-next. :) For patches fixing this, please
> include these lines (but double-check the "Fixes" first):
> 

I think this is a false postive as the subsequent check 'if
(!is_mt7915(&dev->mt76) && i == 3)' should break array "offs" of 8.

Ryder

> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Addresses-Coverity-ID: 1527801 ("Memory - illegal accesses")
> Fixes: 417a4534d223 ("mt76: mt7915: update mt7915_chan_mib_offs for
> mt7916")
> 
> Thanks for your attention!
> 