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Wed, 30 Apr 2025 00:59:15 -0700 (PDT) Received: from localhost ([196.207.164.177]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3a073e5da02sm16350707f8f.93.2025.04.30.00.59.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Apr 2025 00:59:14 -0700 (PDT) Date: Wed, 30 Apr 2025 10:59:11 +0300 From: Dan Carpenter To: Zhongkun He Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@suse.com, yosry.ahmed@linux.dev, muchun.song@linux.dev, yuzhao@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3 2/3] mm: add max swappiness arg to lru_gen for anonymous memory only Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: AC744A0009 X-Stat-Signature: odo6b9drrryyk9nww38yifzh64n59kr1 X-Rspam-User: X-HE-Tag: 1745999956-392499 X-HE-Meta: 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 H8wxBNfu Z4fCi740rp48Q468fHWxo0mBQKw== 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: On Wed, Apr 09, 2025 at 03:06:19PM +0800, Zhongkun He wrote: > + /* set by userspace for anonymous memory only */ > + if (!strncmp("max", swap_string, sizeof("max"))) { This pattern of strncmp("foo", str, sizeof("foo")) is exactly the same as strcmp(). It doesn't provide any additional security. The strncmp() function is meant for matching string prefixes and it's a relatively common bug to do this: intended: if (strcmp(string, "prefix", sizeof("prefix") - 1) == 0) { actual: if (strcmp(string, "prefix", sizeof("prefix")) == 0) { I have a static checker warning for these: https://lore.kernel.org/all/30210ed77b40b4b6629de659cb56b9ec7832c447.1744452787.git.dan.carpenter@linaro.org/ If people deliberately misuse the function then it makes it trickier to tell accidental mistakes from deliberate mistakes. regards, dan carpenter