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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id m11sm1742495pgn.56.2021.07.27.14.16.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jul 2021 14:16:50 -0700 (PDT) From: Kees Cook To: linux-hardening@vger.kernel.org Cc: Kees Cook , "Gustavo A. R. Silva" , Keith Packard , Greg Kroah-Hartman , Andrew Morton , linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev, linux-block@vger.kernel.org, linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com Subject: [PATCH 37/64] string.h: Introduce memset_after() for wiping trailing members/padding Date: Tue, 27 Jul 2021 13:58:28 -0700 Message-Id: <20210727205855.411487-38-keescook@chromium.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210727205855.411487-1-keescook@chromium.org> References: <20210727205855.411487-1-keescook@chromium.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2359; h=from:subject; bh=b9cZC+rDD66z1p4TxzACgUY06GpnBkPGzRd2vUJnnzo=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBhAHOIfqyzMaVVJ7fOFmkjuM928F3ZrP6Vj5vJQu9j TGA+E1GJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYQBziAAKCRCJcvTf3G3AJvL4D/ 432CWZcCqOkVhZ6rWzVtqmSaSBdcUlSVZvNTubv+qk3MAjGXh0WePvQ/w470x2ODfGCERhFWEDFlQj 68DffRJeemD9mQNtxja/G+yKlfKQtqj2GsW7tkAYMYGdzk44ucXmoA6jnRW6vcayOBno0Ak7JtF4lG m7CwO3b7xHmECqmbPERBBHV/EFy/4S7JgLqoPni03PW1KgZDyCWqbwmB04HSW1ssZRyLMd4s3QMY1T +9uiq7oHu8jR42VT7YaiZc18izUh7AQddCZBlvqcHK6sPbsh+klX5zZS9n02ODAklfDkBGB2gb1tzk qTxXC88avclTCkPd2GBEUQEctsttYoNcK4xZ3zRj+wlfk6n2j/Aj/ysxug7cILnKKFV1GD6Yf8nsLg 2k2xEUpWUhhQ6fcZqBd7cBs5gIDYK2zreDrTKcqVFSQ0lX6w9ZyGULXQjv3ILYDHDHvd1PewBgByhA 8aurJtfihL4zDAjHyVugkZ+nfaAmQVaovogYrWCCXoxbMKSIxExx4nWszpvOPpR1mX+l7gYP24rMp1 l768YtsiX/jU5xOMRn5iJGLFogebnye0HYfk45A60bKdiGZmynlnz5gGZL9zYD/aSJOhSfF3kz5hcE XG0Q1qnKtvYm975U6RI0dZPUWK34kAgIzA9fINgzTL6Q+FxQr5sF43MKxRyQ== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org A common idiom in kernel code is to wipe the contents of a structure after a given member. This includes places where there is trailing struct padding. These open-coded cases are usually difficult to read and very sensitive to struct layout changes. Introduce a new helper, memset_after() that takes the target struct instance, the byte to write, and the member name after which the zeroing should start. Signed-off-by: Kees Cook --- include/linux/string.h | 12 ++++++++++++ lib/test_memcpy.c | 12 ++++++++++++ 2 files changed, 24 insertions(+) diff --git a/include/linux/string.h b/include/linux/string.h index cbe889e404e2..4f9f67505f70 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -272,6 +272,18 @@ static __always_inline void memcpy_and_pad(void *dest, size_t dest_len, memcpy(dest, src, dest_len); } +/** + * memset_after - Set a value after a struct member to the end of a struct + * + * @obj: Address of target struct instance + * @v: Byte value to repeatedly write + * @member: after which struct member to start writing bytes + */ +#define memset_after(obj, v, member) do { \ + memset((u8 *)(obj) + offsetofend(typeof(*(obj)), member), v, \ + sizeof(*(obj)) - offsetofend(typeof(*(obj)), member)); \ +} while (0) + /** * str_has_prefix - Test if a string has a given prefix * @str: The string to test diff --git a/lib/test_memcpy.c b/lib/test_memcpy.c index 7c64120a68a9..f52b284f4410 100644 --- a/lib/test_memcpy.c +++ b/lib/test_memcpy.c @@ -223,6 +223,13 @@ static int __init test_memset(void) 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, }, }; + struct some_bytes after = { + .data = { 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x72, + 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, + 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, + 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, + }, + }; struct some_bytes dest = { }; int count, value; u8 *ptr; @@ -254,6 +261,11 @@ static int __init test_memset(void) memset(ptr++, value++, count++); compare("argument side-effects", dest, three); + /* Verify memset_after() */ + dest = control; + memset_after(&dest, 0x72, three); + compare("memset_after()", dest, after); + return 0; #undef TEST_OP }