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userfaultfd: shmem: add i_size checks

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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.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 4c27fe4c4c ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Signed-off-by: Andrea Arcangeli <[email protected]>
Reviewed-by: Mike Rapoport <[email protected]>
Reviewed-by: Hugh Dickins <[email protected]>
Reported-by: Jann Horn <[email protected]>
Cc: <[email protected]>
Cc: "Dr. David Alan Gilbert" <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: [email protected]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Andrea Arcangeli 2018-11-30 14:09:37 -08:00 • committed by Linus Torvalds
commit e2a50c1f64
2 changed files with 40 additions and 4 deletions
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26
mm/userfaultfd.c
View file

@ -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);