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From:   Steve French <smfrench@gmail.com>
Date:   Sat, 13 Jun 2020 16:31:02 -0500
Message-ID: <CAH2r5msU3Oq4swZ2wkUHgNAW1BAM33NT01YEdaGWKSCK+NX-JQ@mail.gmail.com>
Subject: Re: [PATCH] cifs: Fix cached_fid refcnt leak in open_shroot
To:     Xiyu Yang <xiyuyang19@fudan.edu.cn>
Cc:     Steve French <sfrench@samba.org>,
        CIFS <linux-cifs@vger.kernel.org>,
        samba-technical <samba-technical@lists.samba.org>,
        LKML <linux-kernel@vger.kernel.org>, yuanxzhang@fudan.edu.cn,
        kjlu@umn.edu, Xin Tan <tanxin.ctf@gmail.com>
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added cc:stable and merged into cifs-2.6.git for-next

On Sat, Jun 13, 2020 at 7:36 AM Xiyu Yang <xiyuyang19@fudan.edu.cn> wrote:
>
> open_shroot() invokes kref_get(), which increases the refcount of the
> "tcon->crfid" object. When open_shroot() returns not zero, it means the
> open operation failed and close_shroot() will not be called to decrement
> the refcount of the "tcon->crfid".
>
> The reference counting issue happens in one normal path of
> open_shroot(). When the cached root have been opened successfully in a
> concurrent process, the function increases the refcount and jump to
> "oshr_free" to return. However the current return value "rc" may not
> equal to 0, thus the increased refcount will not be balanced outside the
> function, causing a refcnt leak.
>
> Fix this issue by setting the value of "rc" to 0 before jumping to
> "oshr_free" label.
>
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  fs/cifs/smb2ops.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 736d86b8a910..28553d45604e 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -763,6 +763,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon,
>                         /* close extra handle outside of crit sec */
>                         SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
>                 }
> +               rc = 0;
>                 goto oshr_free;
>         }
>
> --
> 2.7.4
>


-- 
Thanks,

Steve