Subject: bug#45595: closed (Re: recvfrom! optional start and end parameter invalid)

From: [email-masked] (GNU bug Tracking System)
Date: Wed, 03 Nov 2021 18:30:03 +0000

Your bug report

#45595: recvfrom! optional start and end parameter invalid

which was filed against the guile package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
45595: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=45595
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: recvfrom! optional start and end parameter invalid
From: lloda <[email-masked]>
To: [email-masked]
Date: Wed, 3 Nov 2021 19:29:03 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

Hi,

Your patch didn't allow for start == end, which is valid as far as I can tell.

With that amended, applied in 1a8294f495cb202f8fcd0f260627c58e7a4c4d10. Thanks!

Subject: recvfrom! optional start and end parameter invalid
From: d4ryus <[email-masked]>
To: [email-masked]
Date: Fri, 1 Jan 2021 12:34:57 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

hi,

the parameter validation for the optional "start" and "end" arguments to
"recvfrom!" are off by one if "end" is passed. From libguile/socket.c
(master commit 64c89458e6):

  ...
  if (SCM_UNBNDP (end))
    cend = SCM_BYTEVECTOR_LENGTH (buf);
  else
    {
      cend = scm_to_size_t (end);
      if (SCM_UNLIKELY (cend >= SCM_BYTEVECTOR_LENGTH (buf)
                        || cend < offset))
        scm_out_of_range (FUNC_NAME, end);
    }
  ...

"end" is the optional end argument, "offset" is 0 or "start" if start
was given. The check must be:

  cend > SCM_BYTEVECTOR_LENGTH (buf) || cend <= offset

to allow filling the last byte in the buffer and verify that start is
not equal to end. A workaround to skip the validation is to not pass
end. But i think a better way would be to always validate start (and
end), if one (or both) of them are passed. A potentional fix is
attached.

If you need any additional information, please let me know.

Thank you for your great work!

-  d4ryus
diff --git a/libguile/socket.c b/libguile/socket.c
index 64354f1f1..d6e676744 100644
--- a/libguile/socket.c
+++ b/libguile/socket.c
@@ -1480,21 +1480,24 @@ SCM_DEFINE (scm_recvfrom, "recvfrom!", 2, 3, 0,
 
   SCM_VALIDATE_BYTEVECTOR (1, buf);
 
-  if (SCM_UNBNDP (start))
-    offset = 0;
-  else
-    offset = scm_to_size_t (start);
-
   if (SCM_UNBNDP (end))
     cend = SCM_BYTEVECTOR_LENGTH (buf);
   else
     {
       cend = scm_to_size_t (end);
-      if (SCM_UNLIKELY (cend >= SCM_BYTEVECTOR_LENGTH (buf)
-                        || cend < offset))
+      if (SCM_UNLIKELY (cend > SCM_BYTEVECTOR_LENGTH (buf)))
         scm_out_of_range (FUNC_NAME, end);
     }
 
+  if (SCM_UNBNDP (start))
+    offset = 0;
+  else
+    {
+      offset = scm_to_size_t (start);
+      if (SCM_UNLIKELY (cend <= offset))
+        scm_out_of_range (FUNC_NAME, start);
+    }
+
   SCM_SYSCALL (rv = recvfrom (fd,
                               SCM_BYTEVECTOR_CONTENTS (buf) + offset,
                               cend - offset, flg,