linux-kernel - Re: Coverity: zram

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Date:   Fri, 11 Nov 2022 19:39:31 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Alexey Romanov <avromanov@...rdevices.ru>,
        linux-kernel@...r.kernel.org, Nick Terrell <terrelln@...com>,
        Minchan Kim <minchan@...nel.org>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Nitin Gupta <ngupta@...are.org>, Jens Axboe <axboe@...nel.dk>,
        Nhat Pham <nphamcs@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-block@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-next@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: Coverity: zram_recompress(): OVERRUN

On (22/11/10 19:15), Kees Cook wrote:
> On Fri, Nov 11, 2022 at 09:26:31AM +0900, Sergey Senozhatsky wrote:
> > On (22/11/10 08:47), coverity-bot wrote:
> > > *** CID 1527270:    (OVERRUN)
> > > drivers/block/zram/zram_drv.c:1727 in zram_recompress()
> > > 1721     		zstrm = zcomp_stream_get(zram->comps[prio]);
> > > 1722     		src = kmap_atomic(page);
> > > 1723     		ret = zcomp_compress(zstrm, src, &comp_len_new);
> > > 1724     		kunmap_atomic(src);
> > > 1725
> > > 1726     		if (ret) {
> > > vvv     CID 1527270:    (OVERRUN)
> > > vvv     Overrunning array "zram->comps" of 4 8-byte elements at element index 4 (byte offset 39) using index "prio" (which evaluates to 4).
> > 
> > Hmm... I don't really see how prio can evaluate to 4.
> 
> Yeah, I agree. This looks like a false positive. I'm not sure why
> Coverity triggered for it. Looking at the extended report, it seems to
> not have any idea that prio_max is correctly bounded.
> 
> Sorry for the noise!

No worries!