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Wed, 01 Jul 2026 18:28:33 -0700 (PDT) Received: from ikb-h07-29-noble.in.iijlab.net ([202.214.97.5]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-847cb94b38asm521961b3a.35.2026.07.01.18.28.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2026 18:28:32 -0700 (PDT) Received: by ikb-h07-29-noble.in.iijlab.net (Postfix, from userid 1010) id E528113C0C7F; Thu, 2 Jul 2026 10:28:31 +0900 (JST) From: Hajime Tazaki To: akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Hajime Tazaki Subject: [PATCH] mm: nommu: add sysctl_max_map_count() check for do_mmap() Date: Thu, 2 Jul 2026 10:28:30 +0900 Message-ID: <20260702012830.667205-1-thehajime@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The sysctl variable vm.max_map_count (sysctl_max_map_count) is not expose under !MMU case but used it wit the default vaule DEFAULT_MAX_MAP_COUNT as a limit of count. This is currently used when a vma entry is split into two chunks (split_vma()) but not used when allocated (do_mmap()). As a result, even if users request a large number of allocate memory, it will keep allocating until OOM happens. This commit introduces a check at the begining of do_mmap in nommu.c to prevent this situation. This is detected with a LTP (Linux Test Project) test, which linked below. Link: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/munmap/munmap04.c Signed-off-by: Hajime Tazaki --- mm/nommu.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/nommu.c b/mm/nommu.c index 5d461ddc3405..815ebefddfae 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1035,6 +1035,9 @@ unsigned long do_mmap(struct file *file, if (ret < 0) return ret; + if (current->mm->map_count >= get_sysctl_max_map_count()) + return -ENOMEM; + /* we ignore the address hint */ addr = 0; len = PAGE_ALIGN(len); -- 2.43.0