[linux] 01/02: mm: remove gup_flags FOLL_WRITE games from __get_user_pages() (CVE-2016-5195)

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carnil pushed a commit to branch jessie-security
in repository linux.

commit 46f7cac7d0e62a88925ed4bb442c9f33e8aae427
Author: Salvatore Bonaccorso <carnil at debian.org>
Date:   Sun Oct 16 09:25:30 2016 +0200

    mm: remove gup_flags FOLL_WRITE games from __get_user_pages() (CVE-2016-5195)
---
 debian/changelog                                   |  2 +
 ...up_flags-FOLL_WRITE-games-from-__get_user.patch | 77 ++++++++++++++++++++++
 debian/patches/series                              |  1 +
 3 files changed, 80 insertions(+)

diff --git a/debian/changelog b/debian/changelog
index e4507f5..c4a90b1 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -5,6 +5,8 @@ linux (3.16.36-1+deb8u2) UNRELEASED; urgency=medium
   * Bluetooth: Fix potential NULL dereference in RFCOMM bind callback
     (CVE-2015-8956)
   * netfilter: x_tables: speed up jump target validation (Closes: #831014)
+  * mm: remove gup_flags FOLL_WRITE games from __get_user_pages()
+    (CVE-2016-5195)
 
  -- Salvatore Bonaccorso <carnil at debian.org>  Tue, 18 Oct 2016 06:39:49 +0200
 
diff --git a/debian/patches/bugfix/all/mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch b/debian/patches/bugfix/all/mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch
new file mode 100644
index 0000000..8505ef0
--- /dev/null
+++ b/debian/patches/bugfix/all/mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch
@@ -0,0 +1,77 @@
+From bd2f56577e4066fcd61eab60d817e86ae8d4c6bf Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds at linux-foundation.org>
+Date: Thu, 13 Oct 2016 13:07:36 -0700
+Subject: [PATCH 01/11] mm: remove gup_flags FOLL_WRITE games from
+ __get_user_pages()
+
+This is an ancient bug that was actually already 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 once
+more try to fix it by checking the pte_dirty() bit properly (and do it
+better).  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.
+
+Reported-and-tested-by: Phil "not Paul" Oester <kernel at linuxace.com>
+Cc: Andy Lutomirski <luto at amacapital.net>
+Cc: Kees Cook <keescook at chromium.org>
+Cc: Oleg Nesterov <oleg at redhat.com>
+Cc: Willy Tarreau <w at 1wt.eu>
+Cc: stable at vger.kernel.org
+Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
+[carnil: backport to 3.16, adjust context]
+---
+ include/linux/mm.h |  1 +
+ mm/gup.c           | 14 ++++++++++++--
+ 2 files changed, 13 insertions(+), 2 deletions(-)
+
+--- a/include/linux/mm.h
++++ b/include/linux/mm.h
+@@ -2029,6 +2029,7 @@ static inline struct page *follow_page(s
+ #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);
+--- a/mm/gup.c
++++ b/mm/gup.c
+@@ -28,6 +28,16 @@ static struct page *no_page_table(struct
+ 	return NULL;
+ }
+ 
++/*
++ * 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)
+ {
+@@ -62,7 +72,7 @@ retry:
+ 	}
+ 	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)) {
+ 		pte_unmap_unlock(ptep, ptl);
+ 		return NULL;
+ 	}
+@@ -302,7 +312,7 @@ static int faultin_page(struct task_stru
+ 	 * reCOWed by userspace write).
+ 	 */
+ 	if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
+-		*flags &= ~FOLL_WRITE;
++	        *flags |= FOLL_COW;
+ 	return 0;
+ }
+ 
diff --git a/debian/patches/series b/debian/patches/series
index 62fdece..d559c95 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -681,6 +681,7 @@ bugfix/all/KEYS-Fix-short-sprintf-buffer-in-proc-keys-show-func.patch
 bugfix/all/scsi-arcmsr-Buffer-overflow-in-arcmsr_iop_message_xf.patch
 bugfix/all/bluetooth-fix-potential-null-dereference-in-rfcomm-b.patch
 bugfix/all/netfilter-x_tables-speed-up-jump-target-validation.patch
+bugfix/all/mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch
 
 # Fix ABI changes
 debian/of-fix-abi-changes.patch

-- 
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