diff mbox series

[1/5] userfaultfd: use ENOENT instead of EFAULT if the atomic copy user fails

Message ID 1548381686-8117-2-git-send-email-tyhicks@canonical.com
State New
Headers show
Series CVE-2018-18397 - tmpfs permissions bypass | expand

Commit Message

Tyler Hicks Jan. 25, 2019, 2:01 a.m. UTC 
From: Andrea Arcangeli <aarcange@redhat.com>

Patch series "userfaultfd shmem updates".

Jann found two bugs in the userfaultfd shmem MAP_SHARED backend: the
lack of the VM_MAYWRITE check and the lack of i_size checks.

Then looking into the above we also fixed the MAP_PRIVATE case.

Hugh by source review also found a data loss source if UFFDIO_COPY is
used on shmem MAP_SHARED PROT_READ mappings (the production usages
incidentally run with PROT_READ|PROT_WRITE, so the data loss couldn't
happen in those production usages like with QEMU).

The whole patchset is marked for stable.

We verified QEMU postcopy live migration with guest running on shmem
MAP_PRIVATE run as well as before after the fix of shmem MAP_PRIVATE.
Regardless if it's shmem or hugetlbfs or MAP_PRIVATE or MAP_SHARED, QEMU
unconditionally invokes a punch hole if the guest mapping is filebacked
and a MADV_DONTNEED too (needed to get rid of the MAP_PRIVATE COWs and
for the anon backend).

This patch (of 5):

We internally used EFAULT to communicate with the caller, switch to
ENOENT, so EFAULT can be used as a non internal retval.

Link: http://lkml.kernel.org/r/20181126173452.26955-2-aarcange@redhat.com
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Hugh Dickins <hughd@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: <stable@vger.kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

CVE-2018-18397

(cherry picked from commit 9e368259ad988356c4c95150fafd1a06af095d98)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 mm/hugetlb.c     | 2 +-
 mm/shmem.c       | 2 +-
 mm/userfaultfd.c | 6 +++---
 3 files changed, 5 insertions(+), 5 deletions(-)
diff mbox series

Patch

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b5bcf50a7d9f..f7a5539f8ddc 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4070,7 +4070,7 @@  int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 
 		/* fallback to copy_from_user outside mmap_sem */
 		if (unlikely(ret)) {
-			ret = -EFAULT;
+			ret = -ENOENT;
 			*pagep = page;
 			/* don't free the page */
 			goto out;
diff --git a/mm/shmem.c b/mm/shmem.c
index 0c6023603b25..a8853fe0c8b6 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2307,7 +2307,7 @@  static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
 				*pagep = page;
 				shmem_inode_unacct_blocks(inode, 1);
 				/* don't free the page */
-				return -EFAULT;
+				return -ENOENT;
 			}
 		} else {		/* mfill_zeropage_atomic */
 			clear_highpage(page);
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 5029f241908f..46c8949e5f8f 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -48,7 +48,7 @@  static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 
 		/* fallback to copy_from_user outside mmap_sem */
 		if (unlikely(ret)) {
-			ret = -EFAULT;
+			ret = -ENOENT;
 			*pagep = page;
 			/* don't free the page */
 			goto out;
@@ -274,7 +274,7 @@  static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 
 		cond_resched();
 
-		if (unlikely(err == -EFAULT)) {
+		if (unlikely(err == -ENOENT)) {
 			up_read(&dst_mm->mmap_sem);
 			BUG_ON(!page);
 
@@ -530,7 +530,7 @@  static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 				       src_addr, &page, zeropage);
 		cond_resched();
 
-		if (unlikely(err == -EFAULT)) {
+		if (unlikely(err == -ENOENT)) {
 			void *page_kaddr;
 
 			up_read(&dst_mm->mmap_sem);