linux-kernel - Re: [PATCH] gfs2: fix overread in the strlcpy of init

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Date:   Wed, 29 Jun 2022 09:56:44 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Dongliang Mu <dzm91@...t.edu.cn>,
        Bob Peterson <rpeterso@...hat.com>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Jean Delvare <khali@...ux-fr.org>,
        syzkaller <syzkaller@...glegroups.com>,
        cluster-devel <cluster-devel@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gfs2: fix overread in the strlcpy of init_names

On Wed, Jun 29, 2022 at 9:33 AM Dongliang Mu <mudongliangabcd@...il.com> wrote:
>
> On Tue, Jun 28, 2022 at 8:06 PM Andreas Gruenbacher <agruenba@...hat.com> wrote:
> >
> > Dongliang Mu,
> >
> > On Tue, Jun 28, 2022 at 8:10 AM Dongliang Mu <dzm91@...t.edu.cn> wrote:
> > > From: Dongliang Mu <mudongliangabcd@...il.com>
> > >
> > > In init_names, strlcpy will overread the src string as the src string is
> > > less than GFS2_FSNAME_LEN(256).
> > >
> > > Fix this by modifying strlcpy back to snprintf, reverting
> > > the commit 00377d8e3842.
> >
> > ... if the source string isn't NULL-terminated. But in that case, the
> > code will still do the same thing with this patch. In other words,
> > this doesn't fix anything. So let's check for NULL termination
> > instead.
>
> Partially yes. Even if the source string is NULL-terminated, strlcpy
> will invoke memcpy to overread the adjacent memory of source string as
> the specified length is longer than source string.

The above statement is incorrect after I double check the
implementation of strlcpy.

The correct fix should be NULL-termination check of src string.

>
> >
> > Thanks,
> > Andreas
> >
> > > Fixes: 00377d8e3842 ("[GFS2] Prefer strlcpy() over snprintf()")
> > > Reported-by: syzkaller <syzkaller@...glegroups.com>
> > > Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> > > ---
> > >  fs/gfs2/ops_fstype.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
> > > index c9b423c874a3..ee29b50d39b9 100644
> > > --- a/fs/gfs2/ops_fstype.c
> > > +++ b/fs/gfs2/ops_fstype.c
> > > @@ -383,8 +383,8 @@ static int init_names(struct gfs2_sbd *sdp, int silent)
> > >         if (!table[0])
> > >                 table = sdp->sd_vfs->s_id;
> > >
> > > -       strlcpy(sdp->sd_proto_name, proto, GFS2_FSNAME_LEN);
> > > -       strlcpy(sdp->sd_table_name, table, GFS2_FSNAME_LEN);
> > > +       snprintf(sdp->sd_proto_name, GFS2_FSNAME_LEN, "%s", proto);
> > > +       snprintf(sdp->sd_table_name, GFS2_FSNAME_LEN, "%s", table);
> > >
> > >         table = sdp->sd_table_name;
> > >         while ((table = strchr(table, '/')))
> > > --
> > > 2.35.1
> > >
> >