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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488cf9e8808sm51409725e9.5.2026.04.09.05.06.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2026 05:06:56 -0700 (PDT) From: David Carlier To: Andrew Morton , Mike Rapoport , Peter Xu Cc: "Liam R . Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Carlier Subject: [PATCH v5] mm/userfaultfd: detect VMA type change after copy retry in mfill_copy_folio_retry() Date: Thu, 9 Apr 2026 13:06:53 +0100 Message-ID: <20260409120653.290386-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: aqfhmgc3ii5ntht4xttochms6uy6zifp X-Rspamd-Queue-Id: A8FE5C0003 X-Rspam-User: X-HE-Tag: 1775736418-839219 X-HE-Meta: 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 pV2r/qAH YTd8cp9LVbII4vVg026JC6l95pN2vS5A3mvr5mfIREu8yc5T7LpifZGjwPH0zXWgbXK5K3MlsYF/1c5X40RdECKzy2V4zzCQE/5KkGMielGbSSqFH+weNL8YxvqxlT5VnZhP1uL1pRO6pn0Fm9wjYPyo7k4gDkQJs5r6zdwWRbTcfOH+IJ5FZ+voHcE+pcMclGuywnkksbOqUFaVXWiIDsHV8WtrxdBDx/1AqNv+Ce8YQCZuKr+1QPnNxrLfB9EcZaTTu3GmyTmryu6ih0mttUdEsX9ZPZvboFtsgwO/+oOjXbNsPZ8GX2DfuWyeVFoTN2wLSyo6AveKeomnMpLkKj5KviewF4/t/lkuqpYANUI2q5ekVVW9BjpebhDqOneocCKI7jmOYumBgK8Fayz6/0JyvE1nqE/GxfJqHxhgs/FfsnpQ418kOC3/vfO0WdwvV3e7ttzs/kLmLG9M= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: mfill_copy_folio_retry() drops mmap_lock for the copy_from_user() call. During this window, the VMA can be replaced with a different type (e.g. hugetlb), making the caller's ops pointer stale. Subsequent use of the stale ops can lead to incorrect folio handling or a kernel crash. Pass the caller's ops into mfill_copy_folio_retry() and compare against the current vma_uffd_ops() after re-acquiring the lock. Return -EAGAIN if they differ so the operation can be retried. Fixes: 59da5c32ffa3 ("userfaultfd: mfill_atomic(): remove retry logic") Signed-off-by: David Carlier --- mm/userfaultfd.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 481ec7eb4442..214923a411c1 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -443,7 +443,9 @@ static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr) return ret; } -static int mfill_copy_folio_retry(struct mfill_state *state, struct folio *folio) +static int mfill_copy_folio_retry(struct mfill_state *state, + const struct vm_uffd_ops *ops, + struct folio *folio) { unsigned long src_addr = state->src_addr; void *kaddr; @@ -465,6 +467,14 @@ static int mfill_copy_folio_retry(struct mfill_state *state, struct folio *folio if (err) return err; + /* + * The VMA type may have changed while the lock was dropped + * (e.g. replaced with a hugetlb mapping), making the caller's + * ops pointer stale. + */ + if (vma_uffd_ops(state->vma) != ops) + return -EAGAIN; + err = mfill_establish_pmd(state); if (err) return err; @@ -495,7 +505,7 @@ static int __mfill_atomic_pte(struct mfill_state *state, * will take care of unlocking if needed. */ if (unlikely(ret)) { - ret = mfill_copy_folio_retry(state, folio); + ret = mfill_copy_folio_retry(state, ops, folio); if (ret) goto err_folio_put; } -- 2.53.0