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From: Dan Carpenter <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Ammar Faizi <[email protected]>,
	GNU/Weeb Mailing List <[email protected]>,
	io-uring Mailing list <[email protected]>,
	Tea Inside Mailing List <[email protected]>,
	Linux Kernel Mailing List <[email protected]>,
	Alviro Iskandar Setiawan <[email protected]>,
	kernel test robot <[email protected]>,
	"Chen, Rong A" <[email protected]>,
	Pavel Begunkov <[email protected]>
Subject: Re: [PATCH io_uring-5.17] io_uring: Fix build error potential reading uninitialized value
Date: Mon, 7 Feb 2022 17:20:46 +0300	[thread overview]
Message-ID: <20220207142046.GP1978@kadam> (raw)
In-Reply-To: <[email protected]>

On Mon, Feb 07, 2022 at 06:45:57AM -0700, Jens Axboe wrote:
> On 2/7/22 4:43 AM, Ammar Faizi wrote:
> > From: Alviro Iskandar Setiawan <[email protected]>
> > 
> > In io_recv() if import_single_range() fails, the @flags variable is
> > uninitialized, then it will goto out_free.
> > 
> > After the goto, the compiler doesn't know that (ret < min_ret) is
> > always true, so it thinks the "if ((flags & MSG_WAITALL) ..."  path
> > could be taken.
> > 
> > The complaint comes from gcc-9 (Debian 9.3.0-22) 9.3.0:
> > ```
> >   fs/io_uring.c:5238 io_recvfrom() error: uninitialized symbol 'flags'
> > ```
> > Fix this by bypassing the @ret and @flags check when
> > import_single_range() fails.
> 
> The compiler should be able to deduce this, and I guess newer compilers
> do which is why we haven't seen this warning before.

No, we disabled GCC's uninitialized variable checking a couple years
back.  Linus got sick of the false positives.  You can still see it if
you enable W=2

fs/io_uring.c: In function ‘io_recv’:
fs/io_uring.c:5252:20: warning: ‘flags’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  } else if ((flags & MSG_WAITALL) && (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC))) {
             ~~~~~~~^~~~~~~~~~~~~~

If you introduce an uninitialized variable bug then likelyhood is the
kbuild-bot will send you a Clang warning or a Smatch warning or both.
I don't think anyone looks at GCC W=2 warnings.

regards,
dan carpenter


  parent reply	other threads:[~2022-02-07 14:46 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
2022-02-07 11:43 ` [PATCH io_uring-5.17] io_uring: Fix build error potential reading uninitialized value Ammar Faizi
2022-02-07 13:45   ` Jens Axboe
2022-02-07 14:05     ` [PATCH io_uring-5.17 v2] io_uring: Clean up a false-positive warning from GCC 9.3.0 Ammar Faizi
2022-02-07 15:38       ` Jens Axboe
2022-02-07 14:20     ` Dan Carpenter [this message]
2022-02-07 14:33       ` [PATCH io_uring-5.17] io_uring: Fix build error potential reading uninitialized value Alviro Iskandar Setiawan
2022-02-07 15:37         ` Jens Axboe

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