diff mbox series

[v3,2/5] block/sheepdog: Use QEMU_NONSTRING for non NUL-terminated arrays

Message ID 20181218175122.3229-3-philmd@redhat.com (mailing list archive)
State New, archived
Headers show
Series Fix strncpy() warnings for GCC8 new -Wstringop-truncation | expand

Commit Message

Philippe Mathieu-Daudé Dec. 18, 2018, 5:51 p.m. UTC 
GCC 8 added a -Wstringop-truncation warning:

  The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
  bug 81117 is specifically intended to highlight likely unintended
  uses of the strncpy function that truncate the terminating NUL
  character from the source string.

This new warning leads to compilation failures:

    CC      block/sheepdog.o
  qemu/block/sheepdog.c: In function 'find_vdi_name':
  qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
       strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1

As described previous to the strncpy() calls, the use of strncpy() is
correct here:

    /* 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);

Use the QEMU_NONSTRING attribute, since this array is intended to store
character arrays that do not necessarily contain a terminating NUL.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 block/sheepdog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Eric Blake Dec. 18, 2018, 6:30 p.m. UTC | #1 
On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
> 
>    The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>    bug 81117 is specifically intended to highlight likely unintended
>    uses of the strncpy function that truncate the terminating NUL
>    character from the source string.
> 
> This new warning leads to compilation failures:
> 
>      CC      block/sheepdog.o
>    qemu/block/sheepdog.c: In function 'find_vdi_name':
>    qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
>         strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1
> 
> As described previous to the strncpy() calls, the use of strncpy() is
> correct here:
> 
>      /* 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);
> 
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.
> 
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>   block/sheepdog.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

> 
> diff --git a/block/sheepdog.c b/block/sheepdog.c
> index 0125df9d49..d4ad6b119d 100644
> --- a/block/sheepdog.c
> +++ b/block/sheepdog.c
> @@ -1224,7 +1224,7 @@ static int find_vdi_name(BDRVSheepdogState *s, const char *filename,
>       SheepdogVdiReq hdr;
>       SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
>       unsigned int wlen, rlen = 0;
> -    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> +    QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
>   
>       fd = connect_to_sdog(s, errp);
>       if (fd < 0) {
>
Michael S. Tsirkin Dec. 18, 2018, 11:09 p.m. UTC | #2 
On Tue, Dec 18, 2018 at 06:51:19PM +0100, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
> 
>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>   bug 81117 is specifically intended to highlight likely unintended
>   uses of the strncpy function that truncate the terminating NUL
>   character from the source string.
> 
> This new warning leads to compilation failures:
> 
>     CC      block/sheepdog.o
>   qemu/block/sheepdog.c: In function 'find_vdi_name':
>   qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
>        strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1
> 
> As described previous to the strncpy() calls, the use of strncpy() is
> correct here:
> 
>     /* 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);
> 
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.
> 
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  block/sheepdog.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/sheepdog.c b/block/sheepdog.c
> index 0125df9d49..d4ad6b119d 100644
> --- a/block/sheepdog.c
> +++ b/block/sheepdog.c
> @@ -1224,7 +1224,7 @@ static int find_vdi_name(BDRVSheepdogState *s, const char *filename,
>      SheepdogVdiReq hdr;
>      SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
>      unsigned int wlen, rlen = 0;
> -    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> +    QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];

In case you decide to respin anyway - this would be
a bit nicer as:
	char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN] QEMU_NONSTRING




>      fd = connect_to_sdog(s, errp);
>      if (fd < 0) {
> -- 
> 2.17.2
Philippe Mathieu-Daudé Dec. 19, 2018, 9:22 a.m. UTC | #3 
Le mer. 19 déc. 2018 00:09, Michael S. Tsirkin <mst@redhat.com> a écrit :

> On Tue, Dec 18, 2018 at 06:51:19PM +0100, Philippe Mathieu-Daudé wrote:
> > GCC 8 added a -Wstringop-truncation warning:
> >
> >   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
> >   bug 81117 is specifically intended to highlight likely unintended
> >   uses of the strncpy function that truncate the terminating NUL
> >   character from the source string.
> >
> > This new warning leads to compilation failures:
> >
> >     CC      block/sheepdog.o
> >   qemu/block/sheepdog.c: In function 'find_vdi_name':
> >   qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256
> equals destination size [-Werror=stringop-truncation]
> >        strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> >        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >   make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1
> >
> > As described previous to the strncpy() calls, the use of strncpy() is
> > correct here:
> >
> >     /* 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);
> >
> > Use the QEMU_NONSTRING attribute, since this array is intended to store
> > character arrays that do not necessarily contain a terminating NUL.
> >
> > Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> > ---
> >  block/sheepdog.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/block/sheepdog.c b/block/sheepdog.c
> > index 0125df9d49..d4ad6b119d 100644
> > --- a/block/sheepdog.c
> > +++ b/block/sheepdog.c
> > @@ -1224,7 +1224,7 @@ static int find_vdi_name(BDRVSheepdogState *s,
> const char *filename,
> >      SheepdogVdiReq hdr;
> >      SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
> >      unsigned int wlen, rlen = 0;
> > -    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> > +    QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
>
> In case you decide to respin anyway - this would be
> a bit nicer as:
>         char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN] QEMU_NONSTRING
>

I'll have to, so OK.
(it looked to me more explicit prepended).


>
>
>
> >      fd = connect_to_sdog(s, errp);
> >      if (fd < 0) {
> > --
> > 2.17.2
>
diff mbox series

Patch

diff --git a/block/sheepdog.c b/block/sheepdog.c
index 0125df9d49..d4ad6b119d 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -1224,7 +1224,7 @@  static int find_vdi_name(BDRVSheepdogState *s, const char *filename,
     SheepdogVdiReq hdr;
     SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
     unsigned int wlen, rlen = 0;
-    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
+    QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
 
     fd = connect_to_sdog(s, errp);
     if (fd < 0) {