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UPSTREAM: mm/shmem: use page_mapping() to detect page cache for uffd continue

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mfill_atomic_install_pte() checks page->mapping to detect whether one page
is used in the page cache.  However as pointed out by Matthew, the page
can logically be a tail page rather than always the head in the case of
uffd minor mode with UFFDIO_CONTINUE.  It means we could wrongly install
one pte with shmem thp tail page assuming it's an anonymous page.

It's not that clear even for anonymous page, since normally anonymous
pages also have page->mapping being setup with the anon vma.  It's safe
here only because the only such caller to mfill_atomic_install_pte() is
always passing in a newly allocated page (mcopy_atomic_pte()), whose
page->mapping is not yet setup.  However that's not extremely obvious
either.

For either of above, use page_mapping() instead.

Bug: 254441685
Link: https://lkml.kernel.org/r/Y2K+y7wnhC4vbnP2@x1n
Fixes: 153132571f02 ("userfaultfd/shmem: support UFFDIO_CONTINUE for shmem")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reported-by: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 93b0d9178743a68723babe8448981f658aebc58e)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I5635ee1a81087e8022169ad1bda1e6d98fe5835f
This commit is contained in:
Peter Xu
2022-11-02 14:41:52 -04:00
committed by Lee Jones
parent f74be44246
commit 8eb30a41f5
1 changed files with 1 additions and 1 deletions
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mm/userfaultfd.c
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@@ -63,7 +63,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
pte_t _dst_pte, *dst_pte; pte_t _dst_pte, *dst_pte;
bool writable = dst_vma->vm_flags & VM_WRITE; bool writable = dst_vma->vm_flags & VM_WRITE;
bool vm_shared = dst_vma->vm_flags & VM_SHARED; bool vm_shared = dst_vma->vm_flags & VM_SHARED;
bool page_in_cache = page->mapping; bool page_in_cache = page_mapping(page);
spinlock_t *ptl; spinlock_t *ptl;
struct inode *inode; struct inode *inode;
pgoff_t offset, max_off; pgoff_t offset, max_off;