kernel: fix CVE-2016-5159 (Dirty COW)

Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>

diff --git a/lfs/linux b/lfs/linux
index e9c7007b1414d3b0a18eba20cf60780a4dc567aa..19d27293437c215c6a133e7707ddb7a90145dd1a 100644 (file)
--- 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 (file)
index 0000000..a47f080
--- /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 <torvalds@linux-foundation.org>
+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 <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>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+Signed-off-by: Jiri Slaby <jslaby@suse.cz>
+---
+ 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
+