qemu-io: Check for trailing chars

Make sure there's not trailing garbage, e.g.
"64k-whatever-i-want-here"
Reported-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

qemu-io-cmds.c

@@ -136,7 +136,14 @@ static char **breakline(char *input, int *count)
 static int64_t cvtnum(const char *s)
 {
     char *end;
-    return qemu_strtosz_suffix(s, &end, QEMU_STRTOSZ_DEFSUFFIX_B);
+    int64_t ret;
+
+    ret = qemu_strtosz_suffix(s, &end, QEMU_STRTOSZ_DEFSUFFIX_B);
+    if (*end != '\0') {
+        /* Detritus at the end of the string */
+        return -EINVAL;
+    }
+    return ret;
 }
 
 #define EXABYTES(x)     ((long long)(x) << 60)