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From:   Wenli Looi <wlooi@ucalgary.ca>
Date:   Sun, 6 Jun 2021 01:09:39 -0700
Message-ID: <CAKe_nd0fNE=+CP4O0cUtOPO5vRC8_gHxjLtH80r_4GO2MW5u4g@mail.gmail.com>
Subject: Re: [PATCH] staging: rtl8723bs: Fix uninitialized variable
To:     "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org
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On Sun, Jun 6, 2021 at 1:00 AM Fabio M. De Francesco
<fmdefrancesco@gmail.com> wrote:
> On Sunday, June 6, 2021 9:51:35 AM CEST Wenli Looi wrote:
> > On Sun, Jun 6, 2021 at 12:13 AM Greg Kroah-Hartman
> >
> > <gregkh@linuxfoundation.org> wrote:
> > > On Sun, Jun 06, 2021 at 12:00:21AM -0700, Wenli Looi wrote:
> > > > Uninitialized struct with invalid pointer causes BUG and prevents access
> > > > point from working. Access point works once I apply this patch.
> > > >
> > > > https://forum.armbian.com/topic/14727-wifi-ap-kernel-bug-in-kernel-5444/
> > > > has more details.
> > > >
> > > > Signed-off-by: Wenli Looi <wlooi@ucalgary.ca>
> > > > ---
> > > >
> > > >  drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c
> > > > b/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c index 2fb80b6eb..
> 7308e1185
> > > > 100644
> > > > --- a/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c
> > > > +++ b/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c
> > > > @@ -2384,7 +2384,7 @@ void rtw_cfg80211_indicate_sta_assoc(struct
> adapter *padapter,
> > > > u8 *pmgmt_frame,> >
> > > >       DBG_871X(FUNC_ADPT_FMT"\n", FUNC_ADPT_ARG(padapter));
> > > >
> > > >       {
> > > >
> > > > -             struct station_info sinfo;
> > > > +             struct station_info sinfo = {};
> > >
> > > What caused this bug to show up?  Did it happen from some other commit?
> > >
> > > Are you sure that all of the fields are being cleared properly here,
> > > what about any "holes" in the structure?
> > >
> > > thanks,
> > > greg k-h
> >
> > I believe this bug has been present since the driver was added to
> > staging:
> > https://github.com/torvalds/linux/commit/
> 554c0a3abf216c991c5ebddcdb2c08689ecd290b
> >
> > It's probably not necessary to zero the entire struct, only
> > sinfo->pertid, which causes problems with the code here:
> > https://github.com/torvalds/linux/blob/
> f5b6eb1e018203913dfefcf6fa988649ad11ad6e/net/wire
> > less/nl80211.c#L5919
> >
> > You can see the following proposed OpenWrt patch
> > (700-wifi-8723bs-ap-bugfix.patch in
> > https://github.com/openwrt/openwrt/pull/4053/files) which sets
> > sinfo.pertid = 0; instead of zeroing the struct.
> >
> > Looking at similar code in a non-staging driver, we can see that the
> > code there zeros the struct using kzalloc():
> > https://github.com/torvalds/linux/blob/
> f5b6eb1e018203913dfefcf6fa988649ad11ad6e/drivers/
> > net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c#L6064
> >
> > Do you think kzalloc() would be preferable?
> >
> You cannot use kzalloc there: 'sinfo' is instantiated automatically on the
> stack. The example you took had a pointer to the struct.

The stack variable could be replaced with code like:

struct station_info *sinfo;if (!sinfo)
sinfo = kzalloc(sizeof(*sinfo), GFP_KERNEL);
...
cfg80211_new_sta(..., sinfo, ...);
kfree(sinfo);

which is what the linked code basically does. I'm not sure if this is preferred?

>
> Fabio
> >
> > Sorry, I'm not familiar with "holes" in the struct.
>
>
>
>