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kernel: add fix for CVE-2016-5195

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Add fix for CVE-2016-5195 to kernel 3.18 and 4.1.
Kernel 4.4 is already fixed since version 4.4.26 which was committed in
32c28a78f7.

Patches taken from Sasha Levin's linux-stable git tree:
http://git.kernel.org/cgit/linux/kernel/git/sashal/linux-stable.git/

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
This commit is contained in:
Stijn Tintel 2016-10-24 05:08:07 +03:00
parent 75e63c2494
commit 839b657a61
2 changed files with 180 additions and 0 deletions
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90
target/linux/generic/patches-3.18/097-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch Normal file
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@ -0,0 +1,90 @@
From e45a502bdeae5a075257c4f061d1ff4ff0821354 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()
[ Upstream commit 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 ]
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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
---
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_NUMA 0x200 /* force NUMA hinting page fault */
#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
+#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
@@ -32,6 +32,16 @@ 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)
{
@@ -66,7 +76,7 @@ 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;
}
@@ -315,7 +325,7 @@ 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;
}

90
target/linux/generic/patches-4.1/097-mm-remove-gup_flags-FOLL_WRITE-games-from-__get_user.patch Normal file
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@ -0,0 +1,90 @@
From c865f98df72112a3997b219bf711bc46c1e90706 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()
[ Upstream commit 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 ]
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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
---
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
@@ -2064,6 +2064,7 @@ static inline struct page *follow_page(s
#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
+#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
@@ -32,6 +32,16 @@ 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)
{
@@ -66,7 +76,7 @@ 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;
}
@@ -315,7 +325,7 @@ 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;
}