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 EL7。
※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`
■SRPM の展開
$ rpm -ivh kernel-3.10.0-327.36.2.el7.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。
※EL7 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_NUMA 0x200 /* force NUMA hinting page fault */
#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
+#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));
+}
+
/**
* follow_page_mask - look up a page descriptor from a user-virtual address
* @vma: vm_area_struct mapping @address
@@ -1569,7 +1579,7 @@ split_fallthrough:
}
if ((flags & FOLL_NUMA) && pte_numa(pte))
goto no_page;
- 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。
※pkgrelease のバージョンを書き換えたいのですが、その変数がいろいろ使われてたり
SOURCES ディレクトリにある linux-3.10.0-327.36.2.el7.tar.xz を指定するポインタにも
なっているため、あえてそのままです。
●Red Hat Enterprise Linux 7 [kernel-3.10.0-327.36.2.el7]
--- kernel.spec.rh 2016-09-28 04:58:07.000000000 +0900
+++ kernel.spec 2016-10-22 04:17:43.531543410 +0900
@@ -282,7 +282,7 @@
License: GPLv2
URL: http://www.kernel.org/
Version: %{rpmversion}
-Release: %{pkg_release}
+Release: %{pkg_release}.tsc
# DO NOT CHANGE THE 'ExclusiveArch' LINE TO TEMPORARILY EXCLUDE AN ARCHITECTURE BUILD.
# SET %%nobuildarches (ABOVE) INSTEAD
ExclusiveArch: noarch i686 x86_64 ppc ppc64 ppc64le s390 s390x
@@ -377,6 +377,7 @@
# empty final patch to facilitate testing of kernel patches
Patch999999: linux-kernel-test.patch
+Patch2000: fix-remove-gup_flags-FOLL_WRITE-games.patch
BuildRoot: %{_tmppath}/kernel-%{KVRA}-root
@@ -685,6 +686,7 @@
cp $RPM_SOURCE_DIR/kernel-%{version}-*.config .
ApplyOptionalPatch linux-kernel-test.patch
+ApplyOptionalPatch fix-remove-gup_flags-FOLL_WRITE-games.patch
# Any further pre-build tree manipulations happen here.
@@ -1530,6 +1532,9 @@
%kernel_variant_files %{with_kdump} kdump
%changelog
+* Sat Oct 22 2016 Makoto Satou <makopi sgv417 jp> [3.10.0-327.36.2.el7.tsc]
+- [security] mm: remove gup_flags FOLL_WRITE games from __get_user_pages() [1384344] {CVE-2016-5195}
+
* Tue Sep 27 2016 Alexander Gordeev <agordeev@redhat.com> [3.10.0-327.36.2.el7]
- [net] add recursion limit to GRO (Sabrina Dubroca) [1378405 1374191] {CVE-2016-7039}
●CentOS 7 [kernel-3.10.0-327.36.2.el7]
--- kernel.spec.org 2016-10-11 06:41:13.000000000 +0900
+++ kernel.spec 2016-10-22 02:01:41.557909497 +0900
@@ -282,7 +282,7 @@
License: GPLv2
URL: http://www.kernel.org/
Version: %{rpmversion}
-Release: %{pkg_release}
+Release: %{pkg_release}.tsc
# DO NOT CHANGE THE 'ExclusiveArch' LINE TO TEMPORARILY EXCLUDE AN ARCHITECTURE BUILD.
# SET %%nobuildarches (ABOVE) INSTEAD
ExclusiveArch: noarch i686 x86_64 ppc ppc64 ppc64le s390 s390x
@@ -380,6 +380,7 @@
Patch1000: debrand-single-cpu.patch
Patch1001: debrand-rh_taint.patch
Patch1002: debrand-rh-i686-cpu.patch
+Patch2000: fix-remove-gup_flags-FOLL_WRITE-games.patch
BuildRoot: %{_tmppath}/kernel-%{KVRA}-root
@@ -691,6 +692,7 @@
ApplyOptionalPatch debrand-single-cpu.patch
ApplyOptionalPatch debrand-rh_taint.patch
ApplyOptionalPatch debrand-rh-i686-cpu.patch
+ApplyOptionalPatch fix-remove-gup_flags-FOLL_WRITE-games.patch
# Any further pre-build tree manipulations happen here.
@@ -1536,6 +1538,9 @@
%kernel_variant_files %{with_kdump} kdump
%changelog
+* Sat Oct 22 2016 Makoto Satou <makopi sgv417 jp> - [3.10.0-327.36.2.el7.tsc]
+- [security] mm: remove gup_flags FOLL_WRITE games from __get_user_pages() [1384344] {CVE-2016-5195}
+
* Mon Oct 10 2016 CentOS Sources <bugs@centos.org> - 3.10.0-327.36.2.el7
- Apply debranding changes
■SourceRPM の作成
$ cd ~/rpmbuild/SPECS/ $ rpmbuild -bs --define 'dist .el7.tsc' kernel.spec
→ここで「–define」で 「dist .el7.tsc」と入れることで、
本当は .el7.tsc という文字列が、RPM に刻まれます。
ただ、CentOS 7 (RHEL 7) 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 .el7.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 .el7.tsc' ~/rpmbuild/SRPMS/kernel-3.10.0-327.36.2.el7.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/x86_64/ # yum localupdate ./*3.10.0-327.36.2.el7.tsc*
■念のため試験
＜アップデート前＞
[admin@centos7 CVE-2016-5195]# echo this is not a test > foo [admin@centos7 CVE-2016-5195]$ uname -r 3.10.0-327.36.2.el7.x86_64 [admin@centos7 CVE-2016-5195]$ ls -la total 12 drwxrwxr-x. 2 admin admin 33 Oct 22 03:17 . drwx------. 6 admin admin 4096 Oct 22 03:17 .. -rw-rw-r--. 1 admin admin 2826 Oct 22 03:17 dirtyc0w.c -rw-r--r--. 1 root root 19 Oct 22 03:18 foo [admin@centos7 CVE-2016-5195]$ cat foo this is not a test [admin@centos7 CVE-2016-5195]$ gcc -lpthread dirtyc0w.c -o dirtyc0w [admin@centos7 CVE-2016-5195]$ ./dirtyc0w foo m00000000000000000 mmap 7f601c0dc000 procselfmem 1800000000 madvise 0 [admin@centos7 CVE-2016-5195]$ cat foo m00000000000000000
→あうあう＾ｑ＾；
＜アップデート後＞
[admin@centos7 CVE-2016-5195]$ uname -r 3.10.0-327.36.2.el7.tsc.x86_64 [admin@centos7 CVE-2016-5195]$ ls -la total 12 drwxrwxr-x. 2 admin admin 33 Oct 22 03:17 . drwx------. 6 admin admin 4096 Oct 22 03:17 .. -rwxrwxr-x. 1 admin admin 13432 Oct 23 03:18 dirtyc0w -rw-rw-r--. 1 admin admin 2826 Oct 22 03:17 dirtyc0w.c -rw-r--r--. 1 root root 19 Oct 22 03:18 foo [admin@centos7 CVE-2016-5195]$ cat foo this is not a test [admin@centos7 CVE-2016-5195]$ ./dirtyc0w foo m00000000000000000 mmap 7f624092d000 procselfmem 1800000000 madvise 0 [admin@centos7 CVE-2016-5195]$ cat foo this is not a test
→せふせふ・ｗ・ｂ
