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Sat, 03 Oct 2026 12:53:28 -0700 (PDT) Received: from casta ([2401:d800:1f1:cd06:9f1f:eeb6:21ad:cee5]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a78e472b48sm3838211a91.8.2026.10.03.12.53.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 03 Oct 2026 12:53:28 -0700 (PDT) From: Nguyen Duy Nhat Anh To: akpm@linux-foundation.org Cc: david@kernel.org, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Nguyen Duy Nhat Anh Subject: [PATCH] mm/gup: fix NULL pointer dereference in fixup_user_fault() Date: Sun, 4 Oct 2026 02:48:46 +0700 Message-ID: <20261003194846.205918-1-neganhat@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In fixup_user_fault(), the 'unlocked' parameter is checked for NULL early on, allowing callers to pass NULL if they do not track whether the mmap lock was dropped. However, if handle_mm_fault() returns VM_FAULT_COMPLETED, line 1597 dereferences 'unlocked' directly (*unlocked = true) without checking if it is NULL. Callers like s390's pci_mmio.c pass NULL for 'unlocked', leading to a kernel NULL pointer dereference when VM_FAULT_COMPLETED occurs. Fix this by checking if 'unlocked' is non-NULL before assigning to it. Signed-off-by: Nguyen Duy Nhat Anh --- mm/gup.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index eb898ea1ee22..64f709a45adc 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1594,7 +1594,8 @@ int fixup_user_fault(struct mm_struct *mm, * could tell the callers so they do not need to unlock. */ mmap_read_lock(mm); - *unlocked = true; + if (unlocked) + *unlocked = true; return 0; } @@ -1608,7 +1609,8 @@ int fixup_user_fault(struct mm_struct *mm, if (ret & VM_FAULT_RETRY) { mmap_read_lock(mm); - *unlocked = true; + if (unlocked) + *unlocked = true; fault_flags |= FAULT_FLAG_TRIED; goto retry; } -- 2.55.0