[sheepdog] Question on the string format of vdiname and tag in LOCK_VDI/GET_VDI_INFO

[Liu Yuan]

On Wed, Dec 04, 2013 at 02:00:19PM +0900, Ryusuke Konishi wrote:
> Hi List,
> 
> It seems that there is ambiguity about string format in vdi name and
> tag name of LOCK_VDI and GET_VDI_INFO requests.
> 
> The find_vdi_name function of dog command ensures that both vdi name
> and tag name are null-terminated in the data buffer with pstrcpy():
> 
>    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> 
>    memset(buf, 0, sizeof(buf));
>    pstrcpy(buf, SD_MAX_VDI_LEN, vdiname);
>    if (tag)
>            pstrcpy(buf + SD_MAX_VDI_LEN, SD_MAX_VDI_TAG_LEN, tag);
> 
> 
> These strings are truncated to the size of buffer - 1 if they are
> longer than it.
> 
> However, find_vdi_name function of the qemu sheepdog driver doesn't
> ensure that filename and tag are null-terminated because it uses
> strncpy():
> 
>    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> 
>    /* This pair of strncpy calls ensures that the buffer is zero-filled,
>     * which is desirable since we'll soon be sending those bytes, and
>     * don't want the send_req to read uninitialized data.
>     */
>    strncpy(buf, filename, SD_MAX_VDI_LEN);
>    strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> 
> These strings are truncated to the size of buffer.
> 
> 
> The current tgt sheepdog driver doesn't ensure it, too:
> 
>    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> 
>    memset(buf, 0, sizeof(buf));
>    strncpy(buf, filename, SD_MAX_VDI_LEN);
>    strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> 
> 
> Is there any guideline for this sort of string data for sheepdog ?
> 

Probably we should adhere to what is being done in dog, that is, all tag and
names are null-terminated. But QEMU code (where tgt driver derives from )is so
old that some early decision is forgotten.

Thanks
Yuan