* Re: Coverity: iwl_dbg_tlv_alloc_fragment(): Control flow issues
2019-11-04 17:37 Coverity: iwl_dbg_tlv_alloc_fragment(): Control flow issues coverity-bot
@ 2019-11-25 9:49 ` Luciano Coelho
0 siblings, 0 replies; 2+ messages in thread
From: Luciano Coelho @ 2019-11-25 9:49 UTC (permalink / raw)
To: coverity-bot, Shahar S Matityahu; +Cc: Gustavo A. R. Silva, linux-next
On Mon, 2019-11-04 at 09:37 -0800, coverity-bot wrote:
> Hello!
>
> This is an experimental automated report about issues detected by Coverity
> from a scan of next-20191031 as part of the linux-next weekly scan project:
> https://scan.coverity.com/projects/linux-next-weekly-scan
>
> You're getting this email because you were associated with the identified
> lines of code (noted below) that were touched by recent commits:
>
> 14124b25780d ("iwlwifi: dbg_ini: implement monitor allocation flow")
>
> Coverity reported the following:
>
> *** CID 1487402: Control flow issues (DEADCODE)
> /drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c: 497 in iwl_dbg_tlv_alloc_fragment()
> 491 pages * PAGE_SIZE);
> 492
> 493 pages = DIV_ROUND_UP(pages, 2);
> 494 }
> 495
> 496 if (!block)
> vvv CID 1487402: Control flow issues (DEADCODE)
> vvv Execution cannot reach this statement: "return -12;".
> 497 return -ENOMEM;
> 498
> 499 frag->physical = physical;
> 500 frag->block = block;
> 501 frag->size = pages * PAGE_SIZE;
> 502
>
> 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):
>
> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Addresses-Coverity-ID: 1487402 ("Control flow issues")
> Fixes: 14124b25780d ("iwlwifi: dbg_ini: implement monitor allocation flow")
>
>
> Thanks for your attention!
Hi,
This is a good catch! We have a loop:
while (pages) {
block = dma_alloc_coherent(fwrt->dev, pages * PAGE_SIZE,
&physical,
GFP_KERNEL | __GFP_NOWARN);
if (block)
break;
IWL_WARN(fwrt, "WRT: Failed to allocate fragment size %lu\n",
pages * PAGE_SIZE);
pages = DIV_ROUND_UP(pages, 2);
}
if (!block)
return -ENOMEM;
Which seems like it will keep trying allocate smaller and smaller
blocks until it succeeds. But "pages" will never become zero (because
of the DIV_ROUND_UP), so if we can't allocate any size and pages
becomes 1, we will keep trying to allocate 1 page until it succeeds.
And in that case, as coverity reported, block will never be NULL.
I'll add a fix to this in our internal tree and it will reach the
mainline following our normal upstream process.
--
Cheers,
Luca.
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