bug#55938: [PATCH] bindat (strz): Error on null byte if packing variable-length string

bug#55938: [PATCH] bindat (strz): Error on null byte if packing variable-length string

[Richard Hansen]

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X-Debbugs-CC: monnier@iro.umontreal.ca

Attached patch:

* lisp/emacs-lisp/bindat.el (strz): Signal an error if a null byte is
encountered while packing a string to a variable-length strz field.
* test/lisp/emacs-lisp/bindat-tests.el (strz): Add tests.

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From f9f93183500aec3a2bf31ba12683861d7295d5b2 Mon Sep 17 00:00:00 2001
From: Richard Hansen <rhansen@rhansen.org>
Date: Mon, 6 Jun 2022 00:52:21 -0400
Subject: [PATCH] bindat (strz): Error on null byte if packing variable-length
 string

* lisp/emacs-lisp/bindat.el (strz): Signal an error if a null byte is
encountered while packing a string to a variable-length strz field.
* test/lisp/emacs-lisp/bindat-tests.el (strz): Add tests.
---
 lisp/emacs-lisp/bindat.el            | 5 +++++
 test/lisp/emacs-lisp/bindat-tests.el | 7 ++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/bindat.el b/lisp/emacs-lisp/bindat.el
index 2d6589b52d..e6740cb6e8 100644
--- a/lisp/emacs-lisp/bindat.el
+++ b/lisp/emacs-lisp/bindat.el
@@ -444,6 +444,11 @@ bindat--pack-strz
   (let* ((v (string-to-unibyte v))
          (len (length v)))
     (dotimes (i len)
+      (if (= (aref v i) 0)
+          ;; Alternatively we could pretend that this was the end of
+          ;; the string and stop packing, but then bindat-length would
+          ;; need to scan the input string looking for a null byte.
+          (error "Null byte encountered in input strz string"))
       (aset bindat-raw (+ bindat-idx i) (aref v i)))
     (setq bindat-idx (+ bindat-idx len 1))))
 
diff --git a/test/lisp/emacs-lisp/bindat-tests.el b/test/lisp/emacs-lisp/bindat-tests.el
index 8bb3baa485..7d1233ded7 100644
--- a/test/lisp/emacs-lisp/bindat-tests.el
+++ b/test/lisp/emacs-lisp/bindat-tests.el
@@ -240,7 +240,12 @@ bindat-test--str-strz-multibyte
 
   (ert-deftest bindat-test--strz-varlen-pack ()
     (should (equal (bindat-pack spec "") "\0"))
-    (should (equal (bindat-pack spec "abc") "abc\0")))
+    (should (equal (bindat-pack spec "abc") "abc\0"))
+    ;; Null bytes in the input string break unpacking.
+    (should-error (bindat-pack spec "\0"))
+    (should-error (bindat-pack spec "\0x"))
+    (should-error (bindat-pack spec "x\0"))
+    (should-error (bindat-pack spec "x\0y")))
 
   (ert-deftest bindat-test--strz-varlen-unpack ()
     (should (equal (bindat-unpack spec "\0") ""))
-- 
2.36.1


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bug#55938: [PATCH] bindat (strz): Error on null byte if packing variable-length string

[Lars Ingebrigtsen]

Richard Hansen <rhansen@rhansen.org> writes:

> * lisp/emacs-lisp/bindat.el (strz): Signal an error if a null byte is
> encountered while packing a string to a variable-length strz field.
> * test/lisp/emacs-lisp/bindat-tests.el (strz): Add tests.

Thanks; pushed to Emacs 29.  (But I changed the `if' to a `when'.)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55938: [PATCH] bindat (strz): Error on null byte if packing variable-length string

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>    (let* ((v (string-to-unibyte v))
>           (len (length v)))
>      (dotimes (i len)
> +      (if (= (aref v i) 0)
> +          ;; Alternatively we could pretend that this was the end of
> +          ;; the string and stop packing, but then bindat-length would
> +          ;; need to scan the input string looking for a null byte.
> +          (error "Null byte encountered in input strz string"))

I suspect a `string-match` looking for NUL would be faster.


        Stefan