From 4bdbf22ee4609aed3cc378f80a1eb656ed68a634 Mon Sep 17 00:00:00 2001 From: Arne Fitzenreiter Date: Sat, 22 Oct 2016 20:20:22 +0200 Subject: [PATCH] kernel: fix CVE-2016-5159 (Dirty COW) Signed-off-by: Arne Fitzenreiter --- lfs/linux | 5 +- ...ags-FOLL_WRITE-games-from-__get_user.patch | 96 +++++++++++++++++++ 2 files changed, 100 insertions(+), 1 deletion(-) create mode 100644 src/patches/linux/0110-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch diff --git a/lfs/linux b/lfs/linux index e9c7007b14..19d2729343 100644 --- a/lfs/linux +++ b/lfs/linux @@ -37,7 +37,7 @@ DIR_APP = $(DIR_SRC)/$(THISAPP) CFLAGS = CXXFLAGS = -PAK_VER = 72 +PAK_VER = 73 DEPS = "" KERNEL_ARCH = $(MACHINE) @@ -206,6 +206,9 @@ ifneq "$(KCFG)" "-headers" cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/linux/0100-crypto-aesni-Add-support-for-192-256-bit-keys-to-AES.patch endif + # fix CVE-2016-5195 (Dirty COW) + cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/linux/0110-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch + # fix empty symbol crc's cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/linux-genksyms_fix_typeof_handling.patch diff --git a/src/patches/linux/0110-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch b/src/patches/linux/0110-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch new file mode 100644 index 0000000000..a47f080794 --- /dev/null +++ b/src/patches/linux/0110-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch @@ -0,0 +1,96 @@ +From a289eb38cfb481de48e36b481c72fb2492c6d242 Mon Sep 17 00:00:00 2001 +From: Linus Torvalds +Date: Thu, 13 Oct 2016 13:07:36 -0700 +Subject: [PATCH] mm: remove gup_flags FOLL_WRITE games from __get_user_pages() + +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 +Acked-by: Hugh Dickins +Reviewed-by: Michal Hocko +Cc: Andy Lutomirski +Cc: Kees Cook +Cc: Oleg Nesterov +Cc: Willy Tarreau +Cc: Nick Piggin +Cc: Greg Thelen +Signed-off-by: Linus Torvalds +Signed-off-by: Jiri Slaby +--- + 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 5aef73c..6f56355 100644 +--- a/include/linux/mm.h ++++ b/include/linux/mm.h +@@ -1964,6 +1964,7 @@ 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 e9f4d40..5c1df12 100644 +--- a/mm/memory.c ++++ b/mm/memory.c +@@ -1449,6 +1449,16 @@ 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); +@@ -1866,7 +1876,7 @@ 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(); + } +-- +2.7.4 + -- 2.39.2