linux-kernel - Re: [PATCH] cifs: fix strcat buffer overflow in smb21_set_oplock

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Message-ID: <CAH2r5msK6yNNm_QbdsFZuB5uS0iNRuqe8gSDKvVAiR0N6E3MWg@mail.gmail.com>
Date:   Mon, 6 May 2019 12:02:07 -0500
From:   Steve French <smfrench@...il.com>
To:     Jeremy Allison <jra@...ba.org>
Cc:     Christoph Probst <kernel@...bst.it>,
        Steve French <sfrench@...ba.org>,
        CIFS <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cifs: fix strcat buffer overflow in smb21_set_oplock_level()

We could always switch it to strncpy :)

In any case - he is correct, it is better than what was there because
we should not strcat unless the array were locked across the whole
function

On Mon, May 6, 2019 at 11:57 AM Jeremy Allison <jra@...ba.org> wrote:
>
> On Mon, May 06, 2019 at 11:53:44AM -0500, Steve French via samba-technical wrote:
> > I think strcpy is clearer - but I don't think it can overflow since if
> > R, W or W were written to "message" then cinode->oplock would be
> > non-zero so we would never strcap "None"
>
> Ahem. In Samba we have :
>
> lib/util/safe_string.h:#define strcpy(dest,src) __ERROR__XX__NEVER_USE_STRCPY___;
>
> Maybe you should do likewise :-).
>
> > On Mon, May 6, 2019 at 10:26 AM Christoph Probst <kernel@...bst.it> wrote:
> > >
> > > Change strcat to strcpy in the "None" case as it is never valid to append
> > > "None" to any other message. It may also overflow char message[5], in a
> > > race condition on cinode if cinode->oplock is unset by another thread
> > > after "RHW" or "RH" had been written to message.
> > >
> > > Signed-off-by: Christoph Probst <kernel@...bst.it>
> > > ---
> > >  fs/cifs/smb2ops.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> > > index c36ff0d..5fd5567 100644
> > > --- a/fs/cifs/smb2ops.c
> > > +++ b/fs/cifs/smb2ops.c
> > > @@ -2936,7 +2936,7 @@ smb21_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock,
> > >                 strcat(message, "W");
> > >         }
> > >         if (!cinode->oplock)
> > > -               strcat(message, "None");
> > > +               strcpy(message, "None");
> > >         cifs_dbg(FYI, "%s Lease granted on inode %p\n", message,
> > >                  &cinode->vfs_inode);
> > >  }
> > > --
> > > 2.1.4
> > >
> >
> >
> > --
> > Thanks,
> >
> > Steve
> >



-- 
Thanks,

Steve