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

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Date:   Mon, 6 May 2019 09:56:58 -0700
From:   Jeremy Allison <jra@...ba.org>
To:     Steve French <smfrench@...il.com>
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()

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
>