malloc: additional unlink hardening for non-small bins [BZ #17344]
Commit Message
Chris Evans has suggested this as a way to stop certain exploits abusing
malloc's metadata processing. My patch is slightly different, the patch
in the bug report has some whitespace changes and locking code which is
not present in master.
Apparently, some downstreams compile malloc with asserts enabled, and
they do not fire, so the validity of the additional checks has in effect
already been tested in the field.
Tested on Fedora 20 x86_64, with no regressions.
Comments
I think it's best practice to put each condition inside a __builtin_expect
separately, rather than to have a complex expression inside it (despite the
contrary example a few lines up). The change seems fine aside from that.
On 09/10/2014 08:10 PM, Roland McGrath wrote:
> I think it's best practice to put each condition inside a __builtin_expect
> separately, rather than to have a complex expression inside it (despite the
> contrary example a few lines up). The change seems fine aside from that.
Thanks. The generated code is the same, so I'm going to commit the
version with two __builtin_expect expressions.
(Eventually, we have to convert malloc/ to __glibc_{,un}likely.)
From 43eb4f76b7736f673c46b1b908e2c5b51004498d Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Wed, 10 Sep 2014 11:00:55 +0200
Subject: [PATCH] malloc: additional unlink hardening for non-small bins [BZ
#17344]
Turn two asserts into a conditional call to malloc_printerr. The
memory locations are accessed later anyway, so the performance
impact is minor.
2014-09-10 Florian Weimer <fweimer@redhat.com>
[BZ #17344]
* malloc/malloc.c (unlink): Turn asserts into a call to
malloc_printerr.
@@ -23,7 +23,7 @@ Version 2.20
16966, 16967, 16977, 16978, 16984, 16990, 16996, 17009, 17022, 17031,
17042, 17048, 17050, 17058, 17061, 17062, 17069, 17075, 17078, 17079,
17084, 17086, 17088, 17092, 17097, 17125, 17135, 17137, 17150, 17153,
- 17187, 17213, 17259, 17261, 17262, 17263, 17319, 17325, 17354.
+ 17187, 17213, 17259, 17261, 17262, 17263, 17319, 17325, 17344, 17354.
* Reverted change of ABI data structures for s390 and s390x:
On s390 and s390x the size of struct ucontext and jmp_buf was increased in
@@ -1418,8 +1418,10 @@ typedef struct malloc_chunk *mbinptr;
BK->fd = FD; \
if (!in_smallbin_range (P->size) \
&& __builtin_expect (P->fd_nextsize != NULL, 0)) { \
- assert (P->fd_nextsize->bk_nextsize == P); \
- assert (P->bk_nextsize->fd_nextsize == P); \
+ if (__builtin_expect (P->fd_nextsize->bk_nextsize != P \
+ || P->bk_nextsize->fd_nextsize != P, 0)) \
+ malloc_printerr (check_action, \
+ "corrupted double-linked list (not small)", P);\
if (FD->fd_nextsize == NULL) { \
if (P->fd_nextsize == P) \
FD->fd_nextsize = FD->bk_nextsize = FD; \
--
1.9.3