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userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry

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When UFFDIO_MOVE encounters a migration PMD entry, it proceeds with
obtaining a folio and accessing it even though the entry is swp_entry_t. 
Add the missing check and let split_huge_pmd() handle migration entries. 
While at it also remove unnecessary folio check.

[surenb@google.com: remove extra folio check, per David]
  Link: https://lkml.kernel.org/r/20250807200418.1963585-1-surenb@google.com
Link: https://lkml.kernel.org/r/20250806220022.926763-1-surenb@google.com
Fixes: adef440691 ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Suren Baghdasaryan 2025-08-06 15:00:22 -07:00 • committed by Andrew Morton
parent cf1b80dc31
commit aba6faec01
1 changed files with 9 additions and 6 deletions
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7
mm/userfaultfd.c
View file

@ -1821,14 +1821,17 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
/* Check if we can move the pmd without splitting it. */
if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
!pmd_none(dst_pmdval)) {
/* Can be a migration entry */
if (pmd_present(*src_pmd)) {
struct folio *folio = pmd_folio(*src_pmd);
if (!folio || (!is_huge_zero_folio(folio) &&
!PageAnonExclusive(&folio->page))) {
if (!is_huge_zero_folio(folio) &&
!PageAnonExclusive(&folio->page)) {
spin_unlock(ptl);
err = -EBUSY;
break;
}
}
spin_unlock(ptl);
split_huge_pmd(src_vma, src_pmd, src_addr);