[PATCH v2 28/32 fix] mm/memory: allow pte_offset_map[_lock]() to fail: fix

From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mike Rapoport <rppt@kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	David Hildenbrand <david@redhat.com>,
	Suren Baghdasaryan <surenb@google.com>,
	Qi Zheng <zhengqi.arch@bytedance.com>,
	Yang Shi <shy828301@gmail.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Peter Xu <peterx@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
	Alistair Popple <apopple@nvidia.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	Ira Weiny <ira.weiny@intel.com>,
	Steven Price <steven.price@arm.com>,
	SeongJae Park <sj@kernel.org>,
	Lorenzo Stoakes <lstoakes@gmail.com>,
	Huang Ying <ying.huang@intel.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Zack Rusin <zackr@vmware.com>, Jason Gunthorpe <jgg@ziepe.ca>,
	Axel Rasmussen <axelrasmussen@google.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Pasha Tatashin <pasha.tatashin@soleen.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Minchan Kim <minchan@kernel.org>,
	Christoph Hellwig <hch@infradead.org>, Song Liu <song@kernel.org>,
	Thomas Hellstrom <thomas.hellstrom@linux.intel.com>,
	Ryan Roberts <ryan.roberts@arm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH v2 28/32 fix] mm/memory: allow pte_offset_map[_lock]() to fail: fix
Date: Thu, 15 Jun 2023 16:10:00 -0700 (PDT)	[thread overview]
Message-ID: <1a4db221-7872-3594-57ce-42369945ec8d@google.com> (raw)
In-Reply-To: <bb548d50-e99a-f29e-eab1-a43bef2a1287@google.com>

__wp_page_copy_user() was liable to call update_mmu_tlb() with NULL
vmf->pte in two places: not a problem today, but could become a problem
later when pte_offset_map_lock() fails.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
Andrew, please add this as a fix patch for later merge into my
"mm/memory: allow" patch in mm-unstable: it's something noticed while
researching the bug Nathan reported, but not so serious - thanks.

 mm/memory.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 4ec46eecefd3..cdadcff5ab26 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2843,7 +2843,8 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
 			 * Other thread has already handled the fault
 			 * and update local tlb only
 			 */
-			update_mmu_tlb(vma, addr, vmf->pte);
+			if (vmf->pte)
+				update_mmu_tlb(vma, addr, vmf->pte);
 			ret = -EAGAIN;
 			goto pte_unlock;
 		}
@@ -2867,7 +2868,8 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
 		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
 		if (unlikely(!vmf->pte || !pte_same(*vmf->pte, vmf->orig_pte))) {
 			/* The PTE changed under us, update local tlb */
-			update_mmu_tlb(vma, addr, vmf->pte);
+			if (vmf->pte)
+				update_mmu_tlb(vma, addr, vmf->pte);
 			ret = -EAGAIN;
 			goto pte_unlock;
 		}
-- 
2.35.3

