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Thu, 31 Jul 2025 09:52:53 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 9109934456634 X-SMAIL-UIID: E9F0BA989AA444DF88B0D3645AEDC517-20250731-095253-1 From: Hillf Danton To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, peterx@redhat.com, lokeshgidra@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot , stable@vger.kernel.org Subject: Re: [PATCH 1/1] userfaultfd: fix a crash when UFFDIO_MOVE handles a THP hole Date: Thu, 31 Jul 2025 09:52:40 +0800 Message-ID: <20250731015241.3576-1-hdanton@sina.com> In-Reply-To: <20250730170733.3829267-1-surenb@google.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: b14e3zcmpnqw8iny9ae7qismr44kyj8y X-Rspam-User: X-Rspamd-Queue-Id: 7DDB9180008 X-Rspamd-Server: rspam02 X-HE-Tag: 1753926778-153978 X-HE-Meta: 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 x+zkVSGg 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: #syz test When UFFDIO_MOVE is used with UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES and it encounters a non-present THP, it fails to properly recognize an unmapped hole and tries to access a non-existent folio, resulting in a crash. Add a check to skip non-present THPs. Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/ Signed-off-by: Suren Baghdasaryan Cc: stable@vger.kernel.org --- mm/userfaultfd.c | 38 +++++++++++++++++++++++--------------- 1 file changed, 23 insertions(+), 15 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index cbed91b09640..60be8080ddd0 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1818,27 +1818,35 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, ptl = pmd_trans_huge_lock(src_pmd, src_vma); if (ptl) { - /* 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 (pmd_present(*src_pmd) || is_pmd_migration_entry(*src_pmd)) { + /* 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)) { + 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 (!folio || (!is_huge_zero_folio(folio) && - !PageAnonExclusive(&folio->page))) { spin_unlock(ptl); - err = -EBUSY; - break; + split_huge_pmd(src_vma, src_pmd, src_addr); + /* The folio will be split by move_pages_pte() */ + continue; } + err = move_pages_huge_pmd(mm, dst_pmd, src_pmd, + dst_pmdval, dst_vma, src_vma, + dst_addr, src_addr); + } else { + /* nothing to do to move a hole */ spin_unlock(ptl); - split_huge_pmd(src_vma, src_pmd, src_addr); - /* The folio will be split by move_pages_pte() */ - continue; + err = 0; } - - err = move_pages_huge_pmd(mm, dst_pmd, src_pmd, - dst_pmdval, dst_vma, src_vma, - dst_addr, src_addr); step_size = HPAGE_PMD_SIZE; } else { if (pmd_none(*src_pmd)) { base-commit: 01da54f10fddf3b01c5a3b80f6b16bbad390c302 -- 2.50.1.552.g942d659e1b-goog