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

From: Kees Cook <[email-masked]>
Date: Fri, 2 Dec 2022 15:04:49 -0800

On Fri, Dec 02, 2022 at 10:56:19PM +0000, Ryder Lee wrote:
> 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.

Ah, okay. What if is_mt7915(&dev->mt76) is always true?

-Kees

> 
> Ryder
> 
> > Reported-by: coverity-bot <[email-masked]>
> > Addresses-Coverity-ID: 1527801 ("Memory - illegal accesses")
> > Fixes: 417a4534d223 ("mt76: mt7915: update mt7915_chan_mib_offs for
> > mt7916")
> > 
> > Thanks for your attention!
> > 

-- 
Kees Cook