diff options
Diffstat (limited to 'kernels/linux-libre-rt/fix-CVE-2016-5195.patch')
| -rw-r--r-- | kernels/linux-libre-rt/fix-CVE-2016-5195.patch | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/kernels/linux-libre-rt/fix-CVE-2016-5195.patch b/kernels/linux-libre-rt/fix-CVE-2016-5195.patch new file mode 100644 index 000000000..598af7f8d --- /dev/null +++ b/kernels/linux-libre-rt/fix-CVE-2016-5195.patch @@ -0,0 +1,90 @@ +author Linus Torvalds <torvalds@linux-foundation.org> 2016-10-13 20:07:36 (GMT) +committer Linus Torvalds <torvalds@linux-foundation.org> 2016-10-18 21:13:29 (GMT) +commit 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 (patch) +tree 9ed601a5726b067beb3e29414c469f88c499a63b +parent 6b25e21fa6f26d0f0d45f161d169029411c84286 (diff) +mm: remove gup_flags FOLL_WRITE games from __get_user_pages() +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> +Diffstat +-rw-r--r-- include/linux/mm.h 1 +-rw-r--r-- mm/gup.c 14 +2 files changed, 13 insertions, 2 deletions +diff --git a/include/linux/mm.h b/include/linux/mm.h +index e9caec6..ed85879 100644 +--- a/include/linux/mm.h ++++ b/include/linux/mm.h +@@ -2232,6 +2232,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma, + #define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */ + #define FOLL_MLOCK 0x1000 /* lock present pages */ + #define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */ ++#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 96b2b2f..22cc22e 100644 +--- a/mm/gup.c ++++ b/mm/gup.c +@@ -60,6 +60,16 @@ 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) + { +@@ -95,7 +105,7 @@ 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; + } +@@ -412,7 +422,7 @@ 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; + } |