Date:   Sun, 9 Jul 2023 15:23:33 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Kalle Valo <kvalo@...nel.org>,
        linux-wireless@...r.kernel.org,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Subject: Re: Build regressions/improvements in v6.4 (wireless/airo)

Hi Randy,

On Sun, Jul 9, 2023 at 3:12 PM Randy Dunlap <rdunlap@...radead.org> wrote:
> On 7/9/23 01:27, Geert Uytterhoeven wrote:
> > On Sun, Jul 9, 2023 at 4:46 AM Randy Dunlap <rdunlap@...radead.org> wrote:
> >> On 6/26/23 01:24, Geert Uytterhoeven wrote:
> >>> On Mon, 26 Jun 2023, Geert Uytterhoeven wrote:
> >>>> JFYI, when comparing v6.4[1] to v6.4-rc7[3], the summaries are:
> >>>>  - build errors: +1/-0
> >>>
> >>>   + /kisskb/src/drivers/net/wireless/cisco/airo.c: error: 'status_rid.currentXmitRate' is used uninitialized [-Werror=uninitialized]:  => 6163:45
> >>
> >> I cannot reproduce this build error. (I don't doubt the problem, just having a problem
> >> making it happen for me.)
> >> I have tried it with gcc-11.1.0, gcc-11.3.0, and gcc-13.1.0.
> >
> > Which is similar to kisskb, using sh4-linux-gcc (GCC) 11.3.0...
> >
> >> I'm surprised that this is the only instance that gcc found/warned about.
> >
> > Indeed.
> >
> >>
> >> I have a patch for this one instance, but there are 40+ instances of
> >>         readStatusRid()
> >>         readConfigRid()
> >>         readSsidRid()
> >>         readStatsRid()
> >>         readCapabilityRid()
> >> that don't check the return status of the function calls.
> >>
> >> I suppose that a patch can quieten the compiler error/warning, but given
> >> the 40+ other problems, it won't make the driver any noticeably better IMO.
> >
> > Indeed...
> >
> >>> sh4-gcc11/sh-allmodconfig
> >>> seen before
> >>>
> >>> This is actually a real issue, and it's been here since basically forever.
> >>>
> >>> drivers/net/wireless/cisco/airo.c:
> >>>
> >>>     static int airo_get_rate(struct net_device *dev,
> >>>                              struct iw_request_info *info,
> >>>                              union iwreq_data *wrqu,
> >>>                              char *extra)
> >>>     {
> >>>             struct iw_param *vwrq = &wrqu->bitrate;
> >>>             struct airo_info *local = dev->ml_priv;
> >>>             StatusRid status_rid;           /* Card status info */
> >>>
> >>>             readStatusRid(local, &status_rid, 1);
> >>>
> >>> ==>         vwrq->value = le16_to_cpu(status_rid.currentXmitRate) * 500000;
> >>>             ...
> >>>     }
> >>>
> >>>     static int readStatusRid(struct airo_info *ai, StatusRid *statr, int lock)
> >>>     {
> >>>             return PC4500_readrid(ai, RID_STATUS, statr, sizeof(*statr), lock);
> >>>     }
> >>>
> >>>     static int PC4500_readrid(struct airo_info *ai, u16 rid, void *pBuf, int len, int lock)
> >>>     {
> >>>             u16 status;
> >>>             int rc = SUCCESS;
> >>>
> >>>             if (lock) {
> >>>                     if (down_interruptible(&ai->sem))
> >>>                             return ERROR;
> >>>
> >>> pBuf output buffer contents not initialized.
> >>>
> >>>             }
> >>>             ...
> >>>     }
> >>>
> >>>
> >>>> [1] http://kisskb.ellerman.id.au/kisskb/branch/linus/head/6995e2de6891c724bfeb2db33d7b87775f913ad1/ (all 160 configs)
> >>>> [3] http://kisskb.ellerman.id.au/kisskb/branch/linus/head/45a3e24f65e90a047bef86f927ebdc4c710edaa1/ (all 160 configs)
> >>
> >> I appreciate the synopsis.  Here's a patch.  WDYT?
> >> ---
> >> From: Randy Dunlap <rdunlap@...radead.org>
> >> Subject: [PATCH] wifi: airo: avoid uninitialized warning in airo_get_rate()
> >>
> >> Quieten a gcc (11.3.0) build error or warning by checking the function
> >> call status and returning -EIO if the function call failed.
> >> This is similar to what several other wireless drivers do for the
> >> SIOCGIWRATE ioctl call.
> >>
> >> drivers/net/wireless/cisco/airo.c: error: 'status_rid.currentXmitRate' is used uninitialized [-Werror=uninitialized]
> >>
> >> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> >> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
> >> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> >> Link: lore.kernel.org/r/39abf2c7-24a-f167-91da-ed4c5435d1c4@...ux-m68k.org
> >> Cc: Kalle Valo <kvalo@...nel.org>
> >> Cc: linux-wireless@...r.kernel.org
> >> ---
> >>  drivers/net/wireless/cisco/airo.c |    5 ++++-
> >>  1 file changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff -- a/drivers/net/wireless/cisco/airo.c b/drivers/net/wireless/cisco/airo.c
> >> --- a/drivers/net/wireless/cisco/airo.c
> >> +++ b/drivers/net/wireless/cisco/airo.c
> >> @@ -6157,8 +6157,11 @@ static int airo_get_rate(struct net_devi
> >>         struct iw_param *vwrq = &wrqu->bitrate;
> >>         struct airo_info *local = dev->ml_priv;
> >>         StatusRid status_rid;           /* Card status info */
> >> +       int ret;
> >>
> >> -       readStatusRid(local, &status_rid, 1);
> >> +       ret = readStatusRid(local, &status_rid, 1);
> >> +       if (ret)
> >> +               return -EIO;
> >
> > That's about the best we can do without further surgery.
> > E.g. PC4500_readrid() should return a proper error code instead of
> > just ERROR/SUCCESS.
> > The case gcc complains about is when lock = 1 and the call to
> > down_interruptible() fails, for which -EBUSY would be appropriate.
>
> Yes, I saw that return value as one of the options.
> I'll change it to that and submit it.

Unfortunately that is not the only possible failure mode.
But it is the one where gcc can _prove_ the output buffer is not initialized ;-)

OMG, PC4500_readrid() can also read from the passed buffer...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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