userfaultfd: use ENOENT instead of EFAULT if the atomic copy user fails

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>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f2e88bb8dd134869a59ea844c3f29a356cb6dd2a..017842b8fcba3d649cec142f3b4dcc3cb5683fce 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4021,7 +4021,7 @@ 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 800482fe6ed6b824cfca28e03908bec4eb6e94e0..a8e4e1cc364ae9a637a3032138f3b7ddb56f9c17 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2286,7 +2286,7 @@ 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 81192701964d36d609d015ce76cf14dbbb1a0dd9..c63c0fc5ecfad888f4c10dcd1a6865dce1c407cd 100644 (file)
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -49,7 +49,7 @@ 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;
@@ -275,7 +275,7 @@ retry:
 
                cond_resched();
 
-               if (unlikely(err == -EFAULT)) {
+               if (unlikely(err == -ENOENT)) {
                        up_read(&dst_mm->mmap_sem);
                        BUG_ON(!page);
 
@@ -521,7 +521,7 @@ retry:
                                       src_addr, &page, zeropage);
                cond_resched();
 
-               if (unlikely(err == -EFAULT)) {
+               if (unlikely(err == -ENOENT)) {
                        void *page_kaddr;
 
                        up_read(&dst_mm->mmap_sem);