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[2001:1c00:3405:d100:e1ff:2c8c:c190:2ee3]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-64b9159ac90sm47948224a12.29.2026.01.03.08.58.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 03 Jan 2026 08:58:16 -0800 (PST) From: Boudewijn van der Heide To: "Liam R . Howlett" Cc: Alice Ryhl , Andrew Ballance , Andrew Morton , maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Boudewijn van der Heide Subject: [PATCH] maple_tree: Add dead node check in mas_dup_alloc() Date: Sat, 3 Jan 2026 17:57:58 +0100 Message-ID: <20260103165758.74094-1-boudewijn@delta-utec.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: hbkx598oku6sp886r9cgz4aeegwij133 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E99B38000D X-HE-Tag: 1767459498-358897 X-HE-Meta: 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 uT7MGIzn joSlCXVSSlLKjmh4Ys0GXjmuhDw7JajzvMrk3l0ipe0k+ld9KF24oM1DWU8O9U3/zNK2uonvvLIw5ympPCqmVkol/ntFPoCCbeuH68JidIvdlh0v7s/c/bg4lxxrQAoXvABKri5Ncf8TpdzD9D7B+UOZ2RmJVk7Sk11L15d28XINruc2zS2lDwS7Q2g4M0cvjF2wZof2+9W8QR2pEwDvc6jomXrJwW0P86+vBGuiospicTaj3VPewg2ns0GjjNzYrwmv0UJsOghDoHMhAw8z1/8SD+kQX8V7RV5CkfLlYuaJ76q9jQtbdsnb07Dqv/EIk4oylgMGTQJXtud2pO/eAaYlq2B9UI/FQnafwqXAwoeL1QdI+2rzdXtf5uzDcrtI7QUGDkTwneXmKOVO7YR5/Kxcu1Z8P/Sptko5EnCIelDBWwyCeh6aPuUIlefLsEytjJ6AYPcqooqO7eToUl7i8pUuU+lwNUIuTO7tR 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: The __mt_dup() function is exported and can be called without internal locking, relying on the caller to provide appropriate synchronization. If a caller fails to hold proper locks, the source tree may be modified concurrently, potentially resulting in dead nodes during traversal. The call stack is: __mt_dup() → mas_dup_build() → mas_dup_alloc() [accesses node->slot[]] The mas_dup_alloc() function may access node slots without first verifying that the node is still alive. If a dead node is encountered, its memory layout may have been switched to the RCU union member, making slot array access undefined behavior as we would be reading from the rcu_head structure instead. Add an explicit dead node check to detect concurrent modification during duplication. When a dead node is detected, return -EBUSY to indicate that the tree is undergoing concurrent modification. Signed-off-by: Boudewijn van der Heide --- Build-tested and boot-tested with QEMU with Buildroot on x86_64. The kernel booted and basic commandline operations work correctly. The race condition this patch addresses is difficult to reproduce in testing, as it requires concurrent tree modifications without proper locking. --- lib/maple_tree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/lib/maple_tree.c b/lib/maple_tree.c index 5aa4c9500018..f623a7aabd53 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -6251,6 +6251,11 @@ static inline void mas_dup_alloc(struct ma_state *mas, struct ma_state *new_mas, /* Allocate memory for child nodes. */ type = mte_node_type(mas->node); new_slots = ma_slots(new_node, type); + if (unlikely(ma_dead_node(node))) { + mas_set_err(mas, -EBUSY); + return; + } + count = mas->node_request = mas_data_end(mas) + 1; mas_alloc_nodes(mas, gfp); if (unlikely(mas_is_err(mas))) -- 2.47.3