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From:   Steve French <smfrench@gmail.com>
Date:   Tue, 7 May 2019 11:13:34 -0500
Message-ID: <CAH2r5mtqkHYbHJkf_LbAjhujnNRQP6Zmkmqhj1dUHomwsc3e=w@mail.gmail.com>
Subject: Re: [PATCH v2] cifs: fix strcat buffer overflow and reduce raciness
 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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Sender: linux-kernel-owner@vger.kernel.org
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merged into cifs-2.6.git for-next

On Tue, May 7, 2019 at 10:17 AM Christoph Probst via samba-technical
<samba-technical@lists.samba.org> wrote:
>
> Change strcat to strncpy in the "None" case to fix a buffer overflow
> when cinode->oplock is reset to 0 by another thread accessing the same
> cinode. It is never valid to append "None" to any other message.
>
> Consolidate multiple writes to cinode->oplock to reduce raciness.
>
> Signed-off-by: Christoph Probst <kernel@probst.it>
> ---
>  fs/cifs/smb2ops.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index c36ff0d..aa61dcf 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -2917,26 +2917,28 @@ smb21_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock,
>                        unsigned int epoch, bool *purge_cache)
>  {
>         char message[5] = {0};
> +       unsigned int new_oplock = 0;
>
>         oplock &= 0xFF;
>         if (oplock == SMB2_OPLOCK_LEVEL_NOCHANGE)
>                 return;
>
> -       cinode->oplock = 0;
>         if (oplock & SMB2_LEASE_READ_CACHING_HE) {
> -               cinode->oplock |= CIFS_CACHE_READ_FLG;
> +               new_oplock |= CIFS_CACHE_READ_FLG;
>                 strcat(message, "R");
>         }
>         if (oplock & SMB2_LEASE_HANDLE_CACHING_HE) {
> -               cinode->oplock |= CIFS_CACHE_HANDLE_FLG;
> +               new_oplock |= CIFS_CACHE_HANDLE_FLG;
>                 strcat(message, "H");
>         }
>         if (oplock & SMB2_LEASE_WRITE_CACHING_HE) {
> -               cinode->oplock |= CIFS_CACHE_WRITE_FLG;
> +               new_oplock |= CIFS_CACHE_WRITE_FLG;
>                 strcat(message, "W");
>         }
> -       if (!cinode->oplock)
> -               strcat(message, "None");
> +       if (!new_oplock)
> +               strncpy(message, "None", sizeof(message));
> +
> +       cinode->oplock = new_oplock;
>         cifs_dbg(FYI, "%s Lease granted on inode %p\n", message,
>                  &cinode->vfs_inode);
>  }
> --
> 2.1.4
>
>


-- 
Thanks,

Steve