Red Hat 社のパッチを待てない子のための、CVE-2016-5195 対応手抜き手順 for EL6。
※たぶんこの手順だと、正式な RPM が公開されたら、問題なく差し替わるはず。
※というか遅くとも一週間でパッチ出るはずだし、逆にもうしないほうがいいと思う。
■ビルド環境の準備
$ vi ~/.rpmmacros
※今回はマルチスレッドでビルドしても大丈夫なので %_smp_mflags はコメントアウトしておく。
%_topdir %(echo $HOME)/rpmbuild #%_smp_mflags -j1 %__arch_install_post /usr/lib/rpm/check-rpaths /usr/lib/rpm/check-buildroot %_tmpfilesdir /usr/lib/tmpfiles.d
■Kernel の SourceRPM を取得してくる
$ mkdir -p ~/rpmbuild/SRPMS/ $ cd ~/rpmbuild/SRPMS/ $ yumdownloader --source kernel-`uname -r`
※yumdownloader でダウンロードできない場合、カスタマーポータル or vault.centos.org からダウンロードする。
■SRPM の展開
$ rpm -ivh kernel-2.6.32-642.6.1.el6.src.rpm
■SOURCES ディレクトリに、[CVE-2016-5195] のパッチを配備
$ cd ~/rpmbuild/SOURCES/ $ vi fix-remove-gup_flags-FOLL_WRITE-games.patch
※此処の表示をコピペしたらエラーします。↑のリンクをお持ち帰りください。
※EL6 用に一部修正してます。オリジナルはこちら。
From: Linus Torvalds <torvalds@linux-foundation.org>
commit 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 upstream.
This is an ancient bug that was actually attempted to be fixed once
(badly) by me eleven years ago in commit 4ceb5db9757a ("Fix
get_user_pages() race for write access") but that was then undone due to
problems on s390 by commit f33ea7f404e5 ("fix get_user_pages bug").
In the meantime, the s390 situation has long been fixed, and we can now
fix it by checking the pte_dirty() bit properly (and do it better). The
s390 dirty bit was implemented in abf09bed3cce ("s390/mm: implement
software dirty bits") which made it into v3.9. Earlier kernels will
have to look at the page state itself.
Also, the VM has become more scalable, and what used a purely
theoretical race back then has become easier to trigger.
To fix it, we introduce a new internal FOLL_COW flag to mark the "yes,
we already did a COW" rather than play racy games with FOLL_WRITE that
is very fundamental, and then use the pte dirty flag to validate that
the FOLL_COW flag is still valid.
Reported-and-tested-by: Phil "not Paul" Oester <kernel@linuxace.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[wt: s/gup.c/memory.c; s/follow_page_pte/follow_page_mask;
s/faultin_page/__get_user_page]
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
include/linux/mm.h | 1 +
mm/memory.c | 14 ++++++++++++--
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 53b0d70..55590f4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1715,6 +1715,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
+#define FOLL_COW 0x4000 /* internal GUP flag */
typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
void *data);
diff --git a/mm/memory.c b/mm/memory.c
index 10cdade..2ca2ee1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1462,6 +1462,16 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);
+/*
+ * FOLL_FORCE can write to even unwritable pte's, but only
+ * after we've gone through a COW cycle and they are dirty.
+ */
+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
+{
+ return pte_write(pte) ||
+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
+}
+
/*
* Do a quick page-table lookup for a single page.
*/
@@ -1569,7 +1579,7 @@ split_fallthrough:
migration_entry_wait(mm, pmd, address);
goto split_fallthrough;
}
- if ((flags & FOLL_WRITE) && !pte_write(pte))
+ if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags))
goto unlock;
page = vm_normal_page(vma, address, pte);
@@ -1877,7 +1887,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
*/
if ((ret & VM_FAULT_WRITE) &&
!(vma->vm_flags & VM_WRITE))
- foll_flags &= ~FOLL_WRITE;
+ foll_flags |= FOLL_COW;
cond_resched();
}
--
2.8.0.rc2.1.gbe9624a
■SPEC にパッチを埋め込む
$ cd ~/rpmbuild/SPECS/ $ cp -piav kernel.spec kernel.spec.org $ vi kernel.spec
※変更点いくつかあるので、Diffを載せてます。
●Red Hat Enterprise Linux 6 [kernel-2.6.32-642.6.1.el6]
--- kernel.spec.rh 2016-08-26 01:19:55.000000000 +0900
+++ kernel.spec 2016-10-22 06:53:30.436166198 +0900
@@ -6,7 +6,7 @@
# and/or a kernel built from an rc or git snapshot, released_kernel should
# be 0.
%define released_kernel 1
-%define dist .el6
+%define dist .el6.tsc
# Versions of various parts
@@ -616,6 +616,7 @@
# empty final patch file to facilitate testing of kernel patches
Patch999999: linux-kernel-test.patch
+Patch2000: fix-remove-gup_flags-FOLL_WRITE-games.patch
BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
@@ -936,6 +937,7 @@
make -f %{SOURCE20} VERSION=%{version} configs
ApplyOptionalPatch linux-kernel-test.patch
+ApplyOptionalPatch fix-remove-gup_flags-FOLL_WRITE-games.patch
# Any further pre-build tree manipulations happen here.
@@ -1740,6 +1742,9 @@
%endif
%changelog
+* Sat Oct 22 2016 Makoto Satou <makopi sgv417 jp> [2.6.32-642.6.1.el6.tsc]
+- [security] mm: remove gup_flags FOLL_WRITE games from __get_user_pages() [1384344] {CVE-2016-5195}
+
* Thu Aug 25 2016 Denys Vlasenko <dvlasenk@redhat.com> [2.6.32-642.6.1.el6]
- [net] tcp: make challenge acks less predictable (Florian Westphal) [1355606 1355607] {CVE-2016-5696}
- [fs] sunrpc: move NO_CRKEY_TIMEOUT to the auth->au_flags (Scott Mayhew) [1366962 1294939]
●CentOS 6 [kernel-2.6.32-642.6.1.el6]
--- kernel.spec.org 2016-10-05 06:06:15.000000000 +0900
+++ kernel.spec 2016-10-22 06:02:34.213320382 +0900
@@ -6,7 +6,7 @@
# and/or a kernel built from an rc or git snapshot, released_kernel should
# be 0.
%define released_kernel 1
-%define dist .el6
+%define dist .el6.tsc
# Versions of various parts
@@ -616,6 +616,7 @@
# empty final patch file to facilitate testing of kernel patches
Patch999999: linux-kernel-test.patch
+Patch2000: fix-remove-gup_flags-FOLL_WRITE-games.patch
BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
@@ -936,6 +937,7 @@
make -f %{SOURCE20} VERSION=%{version} configs
ApplyOptionalPatch linux-kernel-test.patch
+ApplyOptionalPatch fix-remove-gup_flags-FOLL_WRITE-games.patch
# Any further pre-build tree manipulations happen here.
@@ -1740,6 +1742,9 @@
%endif
%changelog
+* Sat Oct 22 2016 Makoto Satou <makopi sgv417 jp> [2.6.32-642.6.1.el6.tsc]
+- [security] mm: remove gup_flags FOLL_WRITE games from __get_user_pages() [1384344] {CVE-2016-5195}
+
* Tue Oct 4 2016 Johnny Hughes <johnny@centos.org> [2.6.32-642.6.1.el6]
- Roll in centOS Branding
■SourceRPM の作成
$ cd ~/rpmbuild/SPECS/ $ rpmbuild -bs --define 'dist .el6.tsc' kernel.spec
→ここで「–define」で 「dist .el6.tsc」と入れることで、
本当は .el6.tsc という文字列が、RPM に刻まれます。
ただ、CentOS 6 (RHEL 6) の kernel.spec では、–define で dist 指定しても
ハードコートされているため反映されません。
そのため、kernel.spec 内の Release 部に、.tsc をハードコートをしてます。
別に入れなくてもいいんですが、自前ビルドしたものがどれなのか明示的に分かる様に
あえて入れております。
SPECファイルのChangelog や define などで .tsc とつけてるのが、自分のサインです。
■Pre-Build の実行
$ rpmbuild -bp --define 'dist .el6.tsc' kernel.spec
→ error: Failed build dependencies が出た場合、
それらをインストールしなければ、ビルドできません。
また、【exit 0】で終了しない場合、何かがおかしいです。
・Patch Fileの内容
・SPEC の記述内容
これらを確認。
■RPM のビルド
$ rpmbuild --rebuild --define 'dist .el6.tsc' ~/rpmbuild/SRPMS/kernel-2.6.32-642.6.1.el6.tsc.src.rpm $ rpmbuild --rebuild --target=noarch --define 'dist .el6.tsc' ~/rpmbuild/SRPMS/kernel-2.6.32-642.6.1.el6.tsc.src.rpm
→ここで「–define」で（ry）
■ビルドした Kernel のインストール
$ su - # cd ~admin/rpmbuild/RPMS/ # yum localupdate ./*/*2.6.32-642.6.1.el6.tsc*
