From: Suren Baghdasaryan Date: Wed, 6 Aug 2025 22:00:22 +0000 (-0700) Subject: userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=aba6faec0103ed8f169be8dce2ead41fcb689446;p=users%2Fjedix%2Flinux-maple.git userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry 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 Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/ Reviewed-by: Peter Xu Acked-by: David Hildenbrand Cc: Andrea Arcangeli Cc: Lokesh Gidra Cc: Signed-off-by: Andrew Morton --- diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index cbed91b096401..45e6290e2e8b3 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1821,13 +1821,16 @@ 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)) { - struct folio *folio = pmd_folio(*src_pmd); - - if (!folio || (!is_huge_zero_folio(folio) && - !PageAnonExclusive(&folio->page))) { - spin_unlock(ptl); - err = -EBUSY; - break; + /* Can be a migration entry */ + if (pmd_present(*src_pmd)) { + struct folio *folio = pmd_folio(*src_pmd); + + if (!is_huge_zero_folio(folio) && + !PageAnonExclusive(&folio->page)) { + spin_unlock(ptl); + err = -EBUSY; + break; + } } spin_unlock(ptl);