[linux] 01/02: mm: remove gup_flags FOLL_WRITE games from __get_user_pages() (CVE-2016-5195)
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Wed Oct 19 18:29:15 UTC 2016
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carnil pushed a commit to branch sid
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commit c5c717224410ddf6830e46c05439adf7783fc1b9
Author: Salvatore Bonaccorso <carnil at debian.org>
Date: Wed Oct 19 17:54:38 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 | 83 ++++++++++++++++++++++
debian/patches/series | 1 +
3 files changed, 86 insertions(+)
diff --git a/debian/changelog b/debian/changelog
index f5989cb..680a4ae 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -158,6 +158,8 @@ linux (4.7.8-1) UNRELEASED; urgency=medium
[ Salvatore Bonaccorso ]
* KEYS: Fix short sprintf buffer in /proc/keys show function (CVE-2016-7042)
+ * mm: remove gup_flags FOLL_WRITE games from __get_user_pages()
+ (CVE-2016-5195)
-- Ben Hutchings <ben at decadent.org.uk> Tue, 11 Oct 2016 22:43:14 +0100
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..b338b4c
--- /dev/null
+++ b/debian/patches/bugfix/all/mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch
@@ -0,0 +1,83 @@
+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>
+---
+ 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 e9caec6a51e9..ed85879f47f5 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 96b2b2fd0fbd..22cc22e7432f 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 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
+ }
+ 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;
+ }
+
+--
+2.10.1.562.ge11b675.dirty
+
diff --git a/debian/patches/series b/debian/patches/series
index 55a40e3..cca79cc 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -118,6 +118,7 @@ bugfix/all/net-add-recursion-limit-to-gro.patch
bugfix/all/posix_acl-clear-sgid-bit-when-setting-file-permissio.patch
bugfix/all/scsi-arcmsr-buffer-overflow-in-arcmsr_iop_message_xf.patch
bugfix/all/KEYS-Fix-short-sprintf-buffer-in-proc-keys-show-func.patch
+bugfix/all/mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch
# ABI maintenance
debian/i8042-revert-abi-break-in-4.7.3.patch
--
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