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From:   Steve French <smfrench@gmail.com>
Date:   Mon, 6 May 2019 11:53:44 -0500
Message-ID: <CAH2r5mtdpOvcE25P2UuNFpOwsNyFiBWRQELQFui+FJGVOOBV8w@mail.gmail.com>
Subject: Re: [PATCH] cifs: fix strcat buffer overflow in smb21_set_oplock_level()
To:     Christoph Probst <kernel@probst.it>
Cc:     CIFS <linux-cifs@vger.kernel.org>,
        Steve French <sfrench@samba.org>,
        samba-technical <samba-technical@lists.samba.org>,
        LKML <linux-kernel@vger.kernel.org>
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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"

On Mon, May 6, 2019 at 10:26 AM Christoph Probst <kernel@probst.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@probst.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