6.15-stable review patch. If anyone has any objections, please let me know.
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From: Suren Baghdasaryan surenb@google.com
commit aba6faec0103ed8f169be8dce2ead41fcb689446 upstream.
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: adef440691ba ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/userfaultfd.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)
--- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1829,13 +1829,16 @@ ssize_t move_pages(struct userfaultfd_ct /* 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)) { - struct folio *folio = pmd_folio(*src_pmd); + /* 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))) { - spin_unlock(ptl); - err = -EBUSY; - break; + if (!is_huge_zero_folio(folio) && + !PageAnonExclusive(&folio->page)) { + spin_unlock(ptl); + err = -EBUSY; + break; + } }
spin_unlock(ptl);