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malloc junk bytes

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Otto Moerbeek

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Oct 14, 2016, 7:41:01 AM10/14/16
to te...@openbsd.org
Hi,

0xdb is better dan 0xd0, since it is unaligned in more cases (think
about the bytes being used as a pointer.

ok?

-Otto

Index: lib/libc/stdlib/malloc.c
===================================================================
RCS file: /cvs/src/lib/libc/stdlib/malloc.c,v
retrieving revision 1.200
diff -u -p -r1.200 malloc.c
--- lib/libc/stdlib/malloc.c 12 Oct 2016 07:36:38 -0000 1.200
+++ lib/libc/stdlib/malloc.c 14 Oct 2016 11:37:44 -0000
@@ -81,8 +81,8 @@
* when the 'J' option is enabled. Use SOME_JUNK right after alloc,
* and SOME_FREEJUNK right before free.
*/
-#define SOME_JUNK 0xd0 /* as in "Duh" :-) */
-#define SOME_FREEJUNK 0xdf
+#define SOME_JUNK 0xdb /* deadbeef */
+#define SOME_FREEJUNK 0xdf /* dead, free */

#define MMAP(sz) mmap(NULL, (sz), PROT_READ | PROT_WRITE, \
MAP_ANON | MAP_PRIVATE, -1, 0)
Index: share/man/man5/malloc.conf.5
===================================================================
RCS file: /cvs/src/share/man/man5/malloc.conf.5,v
retrieving revision 1.7
diff -u -p -r1.7 malloc.conf.5
--- share/man/man5/malloc.conf.5 6 Jul 2016 20:32:02 -0000 1.7
+++ share/man/man5/malloc.conf.5 14 Oct 2016 11:37:45 -0000
@@ -84,10 +84,8 @@ Increase the junk level by one if it is
.Dq Less junking .
Decrease the junk level by one if it is larger than 0.
Junking writes some junk bytes into the area allocated.
-Currently junk is bytes of 0xd0 when allocating; this is pronounced
-.Dq Duh .
-\&:-)
-Freed chunks are filled with 0xdf.
+Currently junk is bytes of 0xdb when allocating;
+freed chunks are filled with 0xdf.
By default the junk level is 1: small chunks are always junked
and the first part of pages is junked after free.
After a delay (if not switched off by the F option),

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