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AJvYcCUR9jMsV0b+PKQehXUeLzz6jwC+jpOZr/oUPzAtDONozazNr2HcQ05inr5h0w0qpQt+ZNrVpFNWFpVqPHmY5RJGfQr3e9K4G+T4hgfevxuLXu+Kxhd53N4Q5h2/duM+6Vc/zsj8SGU2382vO5nkywdnbxjjxIdL3N3PnRhPUrGW2nk1q4ReSn5BZ3LvaIumNE7fMPniAdxSSiSWvQsp1qqRZT6iARzyvIQgz2sJyGugD7oWO2/w6mMAM7dzgluxBOcMdQrBGon/COlH+teUzsQ1LJPd+0R4p1l6pViBn0CJQXKzFjzF/g72Mx/vBdMPMBM0KUgT1w== X-Gm-Message-State: AOJu0YwjE/5QeWA0qxrz05lY2BQVhSxFfB8obUGi/6vAu16MfPrCBMz8 2UFd2AO63kUMrVqoQVxv5uEmsTmpy9iSAyhQk8OAHXsevqXfrEsu X-Google-Smtp-Source: AGHT+IGTYP+13dgbaXUTcOaiyJPHukRZsfD9pPSgLtBCe0th4rvzpLqZDHRAsUFno3V6NU5AaOlIiQ== X-Received: by 2002:a05:6a20:a105:b0:1c0:f2d9:a452 with SMTP id adf61e73a8af0-1c4a12a2e61mr4874235637.13.1722220801130; Sun, 28 Jul 2024 19:40:01 -0700 (PDT) Received: from localhost.localdomain ([223.104.210.31]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2cf28c55a38sm7332247a91.10.2024.07.28.19.39.42 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Jul 2024 19:40:00 -0700 (PDT) From: Yafang Shao To: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org, ebiederm@xmission.com, alexei.starovoitov@gmail.com, rostedt@goodmis.org, catalin.marinas@arm.com, 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 v4 05/11] mm/util: Fix possible race condition in kstrdup() Date: Mon, 29 Jul 2024 10:37:13 +0800 Message-Id: <20240729023719.1933-6-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20240729023719.1933-1-laoar.shao@gmail.com> References: <20240729023719.1933-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@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);