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AJvYcCXxuxyhvqI2J/PjueOpySFIoVQe63OloLy6GyrGlIyvbmlNkzACvzAKlJoagrGW9AatvZmVx4vPNt32/BTy/2xPfUmoLQgvn6BebtZ069tsQwP9PVJG6OYvW5gwiX7KkxGs5S2Cb3v7iGKVCG6UvkMl4PTNqHD6Cm4kqjRF7mPgHCPsYfkNAeRODzv2yWyammJJM2pyALrYgcOGzvl22gzRl5xvlo9vB4/6b345+rzwielhNckGY4uVDWgS4NTUu/ZQMF51KpySm/QmdKjTX85O5hKQ2VwFxR67Ix9rBD76BWYaWroUdA2Q+nXBG6zj1VjzazX62g== X-Gm-Message-State: AOJu0YwkwzE1U2ys8lCr4e6V4QE+SDI+rh4ZVOtt8WxZY34Lb4bEK4LX yJ3EbI78zu9ZYWlargvOHTxA48j0iPOfHUNtSwT7QxJMHb1zD6KJwW2WfpyU X-Google-Smtp-Source: AGHT+IGPBhm+odN2LJAX3QWj+Jlu2WkC5FUNop9iFT0Xeg6XFGC2MN7wYjSEAKCdXzo9nJ50WQHXKg== X-Received: by 2002:a05:6808:1789:b0:3d2:19da:9573 with SMTP id 5614622812f47-3d51b97ee20mr8962729b6e.15.1718937089513; Thu, 20 Jun 2024 19:31:29 -0700 (PDT) Received: from localhost.localdomain ([39.144.105.24]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-706511944d2sm332488b3a.70.2024.06.20.19.31.19 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Jun 2024 19:31:29 -0700 (PDT) From: Yafang Shao To: torvalds@linux-foundation.org Cc: ebiederm@xmission.com, alexei.starovoitov@gmail.com, rostedt@goodmis.org, catalin.marinas@arm.com, akpm@linux-foundation.org, penguin-kernel@i-love.sakura.ne.jp, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, audit@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, Yafang Shao Subject: [PATCH v3 05/11] mm/util: Fix possible race condition in kstrdup() Date: Fri, 21 Jun 2024 10:29:53 +0800 Message-Id: <20240621022959.9124-6-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20240621022959.9124-1-laoar.shao@gmail.com> References: <20240621022959.9124-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In kstrdup(), it is critical to ensure that the dest string is always NUL-terminated. However, potential race condidtion can occur between a writer and a reader. Consider the following scenario involving task->comm: reader writer len = strlen(s) + 1; strlcpy(tsk->comm, buf, sizeof(tsk->comm)); memcpy(buf, s, len); In this case, there is a race condition between the reader and the writer. The reader calculate the length of the string `s` based on the old value of task->comm. However, during the memcpy(), the string `s` might be updated by the writer to a new value of task->comm. If the new task->comm is larger than the old one, the `buf` might not be NUL-terminated. This can lead to undefined behavior and potential security vulnerabilities. Let's fix it by explicitly adding a NUL-terminator. Signed-off-by: Yafang Shao Cc: Andrew Morton --- mm/util.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/util.c b/mm/util.c index c9e519e6811f..41c7875572ed 100644 --- a/mm/util.c +++ b/mm/util.c @@ -60,8 +60,14 @@ char *kstrdup(const char *s, gfp_t gfp) len = strlen(s) + 1; buf = kmalloc_track_caller(len, gfp); - if (buf) + if (buf) { memcpy(buf, s, len); + /* During memcpy(), the string might be updated to a new value, + * which could be longer than the string when strlen() is + * called. Therefore, we need to add a null termimator. + */ + buf[len - 1] = '\0'; + } return buf; } EXPORT_SYMBOL(kstrdup);