cifs: check rsp for NULL before dereferencing in SMB2_open

In SMB2_open there are several paths where the SendReceive2
call will return an error before it sets rsp_iov.iov_base
thus leaving iov_base uninitialized.

Thus we need to check rsp before we dereference it in
the call to get_rfc1002_length().

A report of this issue was previously reported in
http://www.spinics.net/lists/linux-cifs/msg12846.html

RH-bugzilla : 1476151

Version 2 :
* Lets properly initialize rsp_iov before we use it.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/smb2pdu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

2017-09-07 17:37 GMT-07:00 Ronnie Sahlberg <lsahlber@redhat.com>:
> In SMB2_open there are several paths where the SendReceive2
> call will return an error before it sets rsp_iov.iov_base
> thus leaving iov_base uninitialized.
>
> Thus we need to check rsp before we dereference it in
> the call to get_rfc1002_length().
>
> A report of this issue was previously reported in
> http://www.spinics.net/lists/linux-cifs/msg12846.html
>
> RH-bugzilla : 1476151
>
> Version 2 :
> * Lets properly initialize rsp_iov before we use it.
>
> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> ---
>  fs/cifs/smb2pdu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
> index 97edb4d376cd..6e7d145d8b2f 100644
> --- a/fs/cifs/smb2pdu.c
> +++ b/fs/cifs/smb2pdu.c
> @@ -1617,7 +1617,7 @@ SMB2_open(const unsigned int xid, struct cifs_open_parms *oparms, __le16 *path,
>         struct cifs_tcon *tcon = oparms->tcon;
>         struct cifs_ses *ses = tcon->ses;
>         struct kvec iov[4];
> -       struct kvec rsp_iov;
> +       struct kvec rsp_iov = {NULL, 0};
>         int resp_buftype;
>         int uni_path_len;
>         __le16 *copy_path = NULL;
> @@ -1746,7 +1746,7 @@ SMB2_open(const unsigned int xid, struct cifs_open_parms *oparms, __le16 *path,
>
>         if (rc != 0) {
>                 cifs_stats_fail_inc(tcon, SMB2_CREATE_HE);
> -               if (err_buf)
> +               if (err_buf && rsp)
>                         *err_buf = kmemdup(rsp, get_rfc1002_length(rsp) + 4,
>                                            GFP_KERNEL);
>                 goto creat_exit;
> --
> 2.13.3
>
> --
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The patch looks correct. Good candidate for stable, I think.

Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>.

Also It seems like we are not checking for the STATUS_STOPPED_ON_SYMLINK error code in smb2_query_symlink().

--
Best regards,
Pavel Shilovsky
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