GNU bug report logs - #8318
int overflow problem in SAFE_ALLOCA, SAFE_ALLOCA_LISP

Previous Next

Full log

View this message in rfc822 format

From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Paul Eggert <eggert <at> cs.ucla.edu>
Subject: bug#8318: closed (fix merged to trunk)
Date: Wed, 23 Mar 2011 22:07:13 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#8318: int overflow problem in SAFE_ALLOCA, SAFE_ALLOCA_LISP

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

The explanation is attached below, along with your original report.
If you require more details, please reply to 8318 <at> debbugs.gnu.org.

-- 
8318: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8318
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: 8310-done <at> debbugs.gnu.org, 8318-done <at> debbugs.gnu.org, 
	8306-done <at> debbugs.gnu.org, 8303-done <at> debbugs.gnu.org, 
	8277-done <at> debbugs.gnu.org, 8298-done <at> debbugs.gnu.org, 
	8290-done <at> debbugs.gnu.org, 8278-done <at> debbugs.gnu.org
Subject: fix merged to trunk
Date: Wed, 23 Mar 2011 15:06:46 -0700

I committed a fix to the trunk for this,
as part of a recent merge (bzr 103721).

[Message part 3 (message/rfc822, inline)]

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: bug-gnu-emacs <at> gnu.org
Subject: int overflow problem in SAFE_ALLOCA, SAFE_ALLOCA_LISP
Date: Tue, 22 Mar 2011 02:12:52 -0700

The SAFE_ALLOCA macro assumes that adding 1 to the integer
variable sa_must_free cannot overflow, but this assumption
is incorrect in some cases.  I plan to commit the following
patch to fix this.

I found this bug using gcc 4.5.2 -O2 -Wstrict-overflow.

* lisp.h (SAFE_ALLOCA, SAFE_ALLOCA_LISP): Avoid 'int' overflow
leading to a memory leak, possible in functions like
load_charset_map_from_file that can allocate an unbounded number
of objects.
=== modified file 'src/lisp.h'
--- src/lisp.h	2011-03-18 04:58:44 +0000
+++ src/lisp.h	2011-03-22 09:04:53 +0000
@@ -3602,7 +3602,7 @@
     else						  \
       {							  \
 	buf = (type) xmalloc (size);			  \
-	sa_must_free++;					  \
+	sa_must_free = 1;				  \
 	record_unwind_protect (safe_alloca_unwind,	  \
 			       make_save_value (buf, 0)); \
       }							  \
@@ -3632,7 +3632,7 @@
 	buf = (Lisp_Object *) xmalloc (size_);		  \
 	arg_ = make_save_value (buf, nelt);		  \
 	XSAVE_VALUE (arg_)->dogc = 1;			  \
-	sa_must_free++;					  \
+	sa_must_free = 1;				  \
 	record_unwind_protect (safe_alloca_unwind, arg_); \
       }							  \
   } while (0)

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.