With MAP_SHARED: recheck the i_size after taking the PT lock, to
serialize against truncate with the PT lock. Delete the page from the
pagecache if the i_size_read check fails.
With MAP_PRIVATE: check the i_size after the PT lock before mapping
anonymous memory or zeropages into the MAP_PRIVATE shmem mapping.
A mostly irrelevant cleanup: like we do the delete_from_page_cache()
pagecache removal after dropping the PT lock, the PT lock is a
spinlock so drop it before the sleepable page lock.
Reviewed-by: Mike Rapoport <r...@linux.ibm.com>
Reviewed-by: Hugh Dickins <hu...@google.com>
Reported-by: Jann Horn <ja...@google.com>
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for
userfaultfd support")
Cc: sta...@vger.kernel.org
Signed-off-by: Andrea Arcangeli <aarca...@redhat.com>
---
mm/shmem.c | 18 ++++++++++++++++--
mm/userfaultfd.c | 26 ++++++++++++++++++++++++--
2 files changed, 40 insertions(+), 4 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 353287412c25..c3ece7a51949 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2214,6 +2214,7 @@ static int shmem_mfill_atomic_pte(struct mm_struct
*dst_mm,
struct page *page;
pte_t _dst_pte, *dst_pte;
int ret;
+ pgoff_t offset, max_off;
ret = -ENOMEM;
if (!shmem_inode_acct_block(inode, 1))
@@ -2251,6 +2252,12 @@ static int shmem_mfill_atomic_pte(struct mm_struct
*dst_mm,
__SetPageSwapBacked(page);
__SetPageUptodate(page);
+ ret = -EFAULT;
+ offset = linear_page_index(dst_vma, dst_addr);
+ max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+ if (unlikely(offset >= max_off))
+ goto out_release;
+
ret = mem_cgroup_try_charge_delay(page, dst_mm, gfp, &memcg, false);
if (ret)
goto out_release;
@@ -2266,8 +2273,14 @@ static int shmem_mfill_atomic_pte(struct mm_struct
*dst_mm,
if (dst_vma->vm_flags & VM_WRITE)
_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
- ret = -EEXIST;
dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+
+ ret = -EFAULT;
+ max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+ if (unlikely(offset >= max_off))
+ goto out_release_uncharge_unlock;
+
+ ret = -EEXIST;
if (!pte_none(*dst_pte))
goto out_release_uncharge_unlock;
@@ -2285,13 +2298,14 @@ static int shmem_mfill_atomic_pte(struct mm_struct
*dst_mm,
/* No need to invalidate - it was non-present before */
update_mmu_cache(dst_vma, dst_addr, dst_pte);
- unlock_page(page);
pte_unmap_unlock(dst_pte, ptl);
+ unlock_page(page);
ret = 0;
out:
return ret;
out_release_uncharge_unlock:
pte_unmap_unlock(dst_pte, ptl);
+ delete_from_page_cache(page);
out_release_uncharge:
mem_cgroup_cancel_charge(page, memcg, false);
out_release:
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 43cf314cfddd..458acda96f20 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -33,6 +33,8 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
void *page_kaddr;
int ret;
struct page *page;
+ pgoff_t offset, max_off;
+ struct inode *inode;
if (!*pagep) {
ret = -ENOMEM;
@@ -73,8 +75,17 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
if (dst_vma->vm_flags & VM_WRITE)
_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
- ret = -EEXIST;
dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+ if (dst_vma->vm_file) {
+ /* the shmem MAP_PRIVATE case requires checking the i_size */
+ inode = dst_vma->vm_file->f_inode;
+ offset = linear_page_index(dst_vma, dst_addr);
+ max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+ ret = -EFAULT;
+ if (unlikely(offset >= max_off))
+ goto out_release_uncharge_unlock;
+ }
+ ret = -EEXIST;
if (!pte_none(*dst_pte))
goto out_release_uncharge_unlock;
@@ -108,11 +119,22 @@ static int mfill_zeropage_pte(struct mm_struct *dst_mm,
pte_t _dst_pte, *dst_pte;
spinlock_t *ptl;
int ret;
+ pgoff_t offset, max_off;
+ struct inode *inode;
_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
dst_vma->vm_page_prot));
- ret = -EEXIST;
dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+ if (dst_vma->vm_file) {
+ /* the shmem MAP_PRIVATE case requires checking the i_size */
+ inode = dst_vma->vm_file->f_inode;
+ offset = linear_page_index(dst_vma, dst_addr);
+ max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+ ret = -EFAULT;
+ if (unlikely(offset >= max_off))
+ goto out_unlock;
+ }
+ ret = -EEXIST;
if (!pte_none(*dst_pte))
goto out_unlock;
set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
