23.06.2020 00:03, Eric Blake wrote:
When snprintf returns the same value as the buffer size, the final
byte was truncated to ensure a NUL terminator.  Fortunately, such long
export names are unusual enough, with no real impact other than what
is displayed to the user.

Fixes: 5c86bdf12089

Oh, I remember myself checking snprintf spec when reviewing this, but
still I missed this thing :(

Reported-by: Max Reitz <mre...@redhat.com>
Signed-off-by: Eric Blake <ebl...@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>

---
  block/nbd.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/nbd.c b/block/nbd.c
index eed160c5cda1..8301fcac0589 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -2009,7 +2009,7 @@ static void nbd_refresh_filename(BlockDriverState *bs)
          len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),
                         "nbd://%s:%s", host, port);
      }
-    if (len > sizeof(bs->exact_filename)) {
+    if (len >= sizeof(bs->exact_filename)) {
          /* Name is too long to represent exactly, so leave it empty. */
          bs->exact_filename[0] = '\0';
      }


Hmm, interesting, that in case of len=0 (no one branch was executed from 
previous
if-else-if, which seems possible) we do nothing. Shouldn't this if actually be
if (!len || len >= sizeof(bs->exact_filename)) {
  /* Name is too long or we have nothing to report */
  bs->exact_filename[0] = '\0';
}

Probably not, as bdrv_refresh_filename() does it anyway prior to calling 
drv->bdrv_refresh_filename().


--
Best regards,
Vladimir

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