From 7862d74a17bb5a4a6d6b0d60d8cf33650b75c92a Mon Sep 17 00:00:00 2001 From: Zoltan HERPAI Date: Fri, 28 Oct 2016 12:40:32 +0200 Subject: generic/4.4: add fix for CVE-2016-5195 Fixes CVE-2016-5195, backport the mm patch into 097- until the kernel version is upgraded. Compile-tested on ar71xx, ramips. Runtime-tested on ramips. Signed-off-by: Zoltan HERPAI --- ...up_flags-FOLL_WRITE-games-from-__get_user.patch | 96 ++++++++++++++++++++++ 1 file changed, 96 insertions(+) create mode 100644 target/linux/generic/patches-4.4/097-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch diff --git a/target/linux/generic/patches-4.4/097-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch b/target/linux/generic/patches-4.4/097-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch new file mode 100644 index 0000000000..101dbf29ac --- /dev/null +++ b/target/linux/generic/patches-4.4/097-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch @@ -0,0 +1,96 @@ +From 1294d355881cc5c3421d24fee512f16974addb6c Mon Sep 17 00:00:00 2001 +From: Linus Torvalds +Date: Thu, 13 Oct 2016 13:07:36 -0700 +Subject: 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: Greg Kroah-Hartman +--- + include/linux/mm.h | 1 + + mm/gup.c | 14 ++++++++++++-- + 2 files changed, 13 insertions(+), 2 deletions(-) + +diff --git a/include/linux/mm.h b/include/linux/mm.h +index cfebb74..f0ffa01 100644 +--- a/include/linux/mm.h ++++ b/include/linux/mm.h +@@ -2112,6 +2112,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma, + #define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */ + #define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */ + #define FOLL_MLOCK 0x1000 /* lock present pages */ ++#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/gup.c b/mm/gup.c +index deafa2c..4b0b7e7 100644 +--- a/mm/gup.c ++++ b/mm/gup.c +@@ -58,6 +58,16 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address, + return -EEXIST; + } + ++/* ++ * 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)); ++} ++ + static struct page *follow_page_pte(struct vm_area_struct *vma, + unsigned long address, pmd_t *pmd, unsigned int flags) + { +@@ -92,7 +102,7 @@ retry: + } + if ((flags & FOLL_NUMA) && pte_protnone(pte)) + goto no_page; +- if ((flags & FOLL_WRITE) && !pte_write(pte)) { ++ if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) { + pte_unmap_unlock(ptep, ptl); + return NULL; + } +@@ -352,7 +362,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma, + * reCOWed by userspace write). + */ + if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE)) +- *flags &= ~FOLL_WRITE; ++ *flags |= FOLL_COW; + return 0; + } + +-- +cgit v0.12 + -- cgit v1.2.3