[PATCH v2 0/4] string: Allow 2-argument strscpy()

[PATCH v2 0/4] string: Allow 2-argument strscpy()

[Kees Cook]

Hi,

v2:
 - add strscpy_pad() coverage
 - fix up ARCH=um to handle the renaming
 - use __must_be_array() to validate sizeof() usage
v1: https://lore.kernel.org/all/20240131055340.work.279-kees@kernel.org/

Make it possible for strscpy() and strscpy_pad() to use 2 arguments,
making "sizeof(dst)" be the the default 3rd argument for the destination
size. This can make future usage much easier to read. Additionally allows
treewide changes to save a bunch of lines:
 1177 files changed, 2455 insertions(+), 3026 deletions(-)

-Kees

Kees Cook (4):
  string: Redefine strscpy_pad() as a macro
  string: Allow 2-argument strscpy()
  string: Allow 2-argument strscpy_pad()
  um: Convert strscpy() usage to 2-argument style

 arch/um/drivers/net_kern.c               |  2 +-
 arch/um/drivers/vector_kern.c            |  2 +-
 arch/um/drivers/vector_user.c            |  4 +-
 arch/um/include/shared/user.h            |  3 +-
 arch/um/os-Linux/drivers/ethertap_user.c |  2 +-
 arch/um/os-Linux/drivers/tuntap_user.c   |  2 +-
 arch/um/os-Linux/umid.c                  |  6 +-
 include/linux/fortify-string.h           | 22 +------
 include/linux/string.h                   | 75 +++++++++++++++++++++++-
 lib/string.c                             |  4 +-
 lib/string_helpers.c                     | 34 -----------
 11 files changed, 87 insertions(+), 69 deletions(-)

-- 
2.34.1

[PATCH v2 1/4] string: Redefine strscpy_pad() as a macro

[Kees Cook]

In preparation for making strscpy_pad()'s 3rd argument optional, redefine
it as a macro. This also has the benefit of allowing greater FORITFY
introspection, as it couldn't see into the strscpy() nor the memset()
within strscpy_pad().

Cc: Andy Shevchenko <andy@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/string.h | 33 +++++++++++++++++++++++++++++++--
 lib/string_helpers.c   | 34 ----------------------------------
 2 files changed, 31 insertions(+), 36 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index ab148d8dbfc1..03f59cf7fe72 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -70,8 +70,37 @@ extern char * strncpy(char *,const char *, __kernel_size_t);
 ssize_t strscpy(char *, const char *, size_t);
 #endif
 
-/* Wraps calls to strscpy()/memset(), no arch specific code required */
-ssize_t strscpy_pad(char *dest, const char *src, size_t count);
+/**
+ * strscpy_pad() - Copy a C-string into a sized buffer
+ * @dest: Where to copy the string to
+ * @src: Where to copy the string from
+ * @count: Size of destination buffer
+ *
+ * Copy the string, or as much of it as fits, into the dest buffer. The
+ * behavior is undefined if the string buffers overlap. The destination
+ * buffer is always %NUL terminated, unless it's zero-sized.
+ *
+ * If the source string is shorter than the destination buffer, zeros
+ * the tail of the destination buffer.
+ *
+ * For full explanation of why you may want to consider using the
+ * 'strscpy' functions please see the function docstring for strscpy().
+ *
+ * Returns:
+ * * The number of characters copied (not including the trailing %NULs)
+ * * -E2BIG if count is 0 or @src was truncated.
+ */
+#define strscpy_pad(dest, src, count)	({			\
+	char *__dst = (dest);						\
+	const char *__src = (src);					\
+	const size_t __count = (count);					\
+	ssize_t __wrote;						\
+									\
+	__wrote = strscpy(__dst, __src, __count);			\
+	if (__wrote >= 0 && __wrote < __count)				\
+		memset(__dst + __wrote + 1, 0, __count - __wrote - 1);	\
+	__wrote;							\
+})
 
 #ifndef __HAVE_ARCH_STRCAT
 extern char * strcat(char *, const char *);
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 7713f73e66b0..606c3099013f 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -825,40 +825,6 @@ char **devm_kasprintf_strarray(struct device *dev, const char *prefix, size_t n)
 }
 EXPORT_SYMBOL_GPL(devm_kasprintf_strarray);
 
-/**
- * strscpy_pad() - Copy a C-string into a sized buffer
- * @dest: Where to copy the string to
- * @src: Where to copy the string from
- * @count: Size of destination buffer
- *
- * Copy the string, or as much of it as fits, into the dest buffer.  The
- * behavior is undefined if the string buffers overlap.  The destination
- * buffer is always %NUL terminated, unless it's zero-sized.
- *
- * If the source string is shorter than the destination buffer, zeros
- * the tail of the destination buffer.
- *
- * For full explanation of why you may want to consider using the
- * 'strscpy' functions please see the function docstring for strscpy().
- *
- * Returns:
- * * The number of characters copied (not including the trailing %NUL)
- * * -E2BIG if count is 0 or @src was truncated.
- */
-ssize_t strscpy_pad(char *dest, const char *src, size_t count)
-{
-	ssize_t written;
-
-	written = strscpy(dest, src, count);
-	if (written < 0 || written == count - 1)
-		return written;
-
-	memset(dest + written + 1, 0, count - written - 1);
-
-	return written;
-}
-EXPORT_SYMBOL(strscpy_pad);
-
 /**
  * skip_spaces - Removes leading whitespace from @str.
  * @str: The string to be stripped.
-- 
2.34.1

[PATCH v2 2/4] string: Allow 2-argument strscpy()

[Kees Cook]

Using sizeof(dst) for the "size" argument in strscpy() is the
overwhelmingly common case. Instead of requiring this everywhere, allow a
2-argument version to be used that will use the sizeof() internally. There
are other functions in the kernel with optional arguments[1], so this
isn't unprecedented, and improves readability. Update and relocate the
kern-doc for strscpy() too.

Adjust ARCH=um build to notice the changed export name, as it doesn't
do full header includes for the string helpers.

This could additionally let us save a few hundred lines of code:
 1177 files changed, 2455 insertions(+), 3026 deletions(-)
with a treewide cleanup using Coccinelle:

@needless_arg@
expression DST, SRC;
@@

        strscpy(DST, SRC
-, sizeof(DST)
        )

Link: https://elixir.bootlin.com/linux/v6.7/source/include/linux/pci.h#L1517 [1]
Reviewed-by: Justin Stitt <justinstitt@google.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/um/include/shared/user.h  |  3 ++-
 include/linux/fortify-string.h | 22 ++-------------------
 include/linux/string.h         | 35 +++++++++++++++++++++++++++++++++-
 lib/string.c                   |  4 ++--
 4 files changed, 40 insertions(+), 24 deletions(-)

diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
index 981e11d8e025..9568cc04cbb7 100644
--- a/arch/um/include/shared/user.h
+++ b/arch/um/include/shared/user.h
@@ -51,7 +51,8 @@ static inline int printk(const char *fmt, ...)
 
 extern int in_aton(char *str);
 extern size_t strlcat(char *, const char *, size_t);
-extern size_t strscpy(char *, const char *, size_t);
+extern size_t sized_strscpy(char *, const char *, size_t);
+#define strscpy(dst, src, size)	sized_strscpy(dst, src, size)
 
 /* Copied from linux/compiler-gcc.h since we can't include it directly */
 #define barrier() __asm__ __volatile__("": : :"memory")
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 89a6888f2f9e..06b3aaa63724 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -215,26 +215,8 @@ __kernel_size_t __fortify_strlen(const char * const POS p)
 }
 
 /* Defined after fortified strnlen() to reuse it. */
-extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy);
-/**
- * strscpy - Copy a C-string into a sized buffer
- *
- * @p: Where to copy the string to
- * @q: Where to copy the string from
- * @size: Size of destination buffer
- *
- * Copy the source string @q, or as much of it as fits, into the destination
- * @p buffer. The behavior is undefined if the string buffers overlap. The
- * destination @p buffer is always NUL terminated, unless it's zero-sized.
- *
- * Preferred to strncpy() since it always returns a valid string, and
- * doesn't unnecessarily force the tail of the destination buffer to be
- * zero padded. If padding is desired please use strscpy_pad().
- *
- * Returns the number of characters copied in @p (not including the
- * trailing %NUL) or -E2BIG if @size is 0 or the copy of @q was truncated.
- */
-__FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, size_t size)
+extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(sized_strscpy);
+__FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const POS q, size_t size)
 {
 	/* Use string size rather than possible enclosing struct size. */
 	const size_t p_size = __member_size(p);
diff --git a/include/linux/string.h b/include/linux/string.h
index 03f59cf7fe72..a21371aa2fd6 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -67,9 +67,42 @@ extern char * strcpy(char *,const char *);
 extern char * strncpy(char *,const char *, __kernel_size_t);
 #endif
 #ifndef __HAVE_ARCH_STRSCPY
-ssize_t strscpy(char *, const char *, size_t);
+ssize_t sized_strscpy(char *, const char *, size_t);
 #endif
 
+/*
+ * The 2 argument style can only be used when dst is an array with a
+ * known size.
+ */
+#define __strscpy0(dst, src, ...)	\
+	sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
+#define __strscpy1(dst, src, size)	sized_strscpy(dst, src, size)
+
+/**
+ * strscpy - Copy a C-string into a sized buffer
+ * @dst: Where to copy the string to
+ * @src: Where to copy the string from
+ * @...: Size of destination buffer (optional)
+ *
+ * Copy the source string @src, or as much of it as fits, into the
+ * destination @dst buffer. The behavior is undefined if the string
+ * buffers overlap. The destination @dst buffer is always NUL terminated,
+ * unless it's zero-sized.
+ *
+ * The size argument @... is only required when @dst is not an array, or
+ * when the copy needs to be smaller than sizeof(@dst).
+ *
+ * Preferred to strncpy() since it always returns a valid string, and
+ * doesn't unnecessarily force the tail of the destination buffer to be
+ * zero padded. If padding is desired please use strscpy_pad().
+ *
+ * Returns the number of characters copied in @dst (not including the
+ * trailing %NUL) or -E2BIG if @size is 0 or the copy from @src was
+ * truncated.
+ */
+#define strscpy(dst, src, ...)	\
+	CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
+
 /**
  * strscpy_pad() - Copy a C-string into a sized buffer
  * @dest: Where to copy the string to
diff --git a/lib/string.c b/lib/string.c
index 6891d15ce991..2869895a1180 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -104,7 +104,7 @@ EXPORT_SYMBOL(strncpy);
 #endif
 
 #ifndef __HAVE_ARCH_STRSCPY
-ssize_t strscpy(char *dest, const char *src, size_t count)
+ssize_t sized_strscpy(char *dest, const char *src, size_t count)
 {
 	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
 	size_t max = count;
@@ -170,7 +170,7 @@ ssize_t strscpy(char *dest, const char *src, size_t count)
 
 	return -E2BIG;
 }
-EXPORT_SYMBOL(strscpy);
+EXPORT_SYMBOL(sized_strscpy);
 #endif
 
 /**
-- 
2.34.1

[PATCH v2 3/4] string: Allow 2-argument strscpy_pad()

[Kees Cook]

Similar to strscpy(), update strscpy_pad()'s 3rd argument to be
optional when the destination is a compile-time known size array.

Cc: Andy Shevchenko <andy@kernel.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/string.h | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index a21371aa2fd6..4f0f27013418 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -78,6 +78,10 @@ ssize_t sized_strscpy(char *, const char *, size_t);
 	sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
 #define __strscpy1(dst, src, size)	sized_strscpy(dst, src, size)
 
+#define __strscpy_pad0(dst, src, ...)	\
+	sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst))
+#define __strscpy_pad1(dst, src, size)	sized_strscpy_pad(dst, src, size)
+
 /**
  * strscpy - Copy a C-string into a sized buffer
  * @dst: Where to copy the string to
@@ -103,6 +107,18 @@ ssize_t sized_strscpy(char *, const char *, size_t);
 #define strscpy(dst, src, ...)	\
 	CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
 
+#define sized_strscpy_pad(dest, src, count)	({			\
+	char *__dst = (dest);						\
+	const char *__src = (src);					\
+	const size_t __count = (count);					\
+	ssize_t __wrote;						\
+									\
+	__wrote = sized_strscpy(__dst, __src, __count);			\
+	if (__wrote >= 0 && __wrote < __count)				\
+		memset(__dst + __wrote + 1, 0, __count - __wrote - 1);	\
+	__wrote;							\
+})
+
 /**
  * strscpy_pad() - Copy a C-string into a sized buffer
  * @dest: Where to copy the string to
@@ -123,17 +139,8 @@ ssize_t sized_strscpy(char *, const char *, size_t);
  * * The number of characters copied (not including the trailing %NULs)
  * * -E2BIG if count is 0 or @src was truncated.
  */
-#define strscpy_pad(dest, src, count)	({			\
-	char *__dst = (dest);						\
-	const char *__src = (src);					\
-	const size_t __count = (count);					\
-	ssize_t __wrote;						\
-									\
-	__wrote = strscpy(__dst, __src, __count);			\
-	if (__wrote >= 0 && __wrote < __count)				\
-		memset(__dst + __wrote + 1, 0, __count - __wrote - 1);	\
-	__wrote;							\
-})
+#define strscpy_pad(dst, src, ...)	\
+	CONCATENATE(__strscpy_pad, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
 
 #ifndef __HAVE_ARCH_STRCAT
 extern char * strcat(char *, const char *);
-- 
2.34.1

[PATCH v2 4/4] um: Convert strscpy() usage to 2-argument style

[Kees Cook]

The ARCH=um build has its own idea about strscpy()'s definition. Adjust
the callers to remove the redundant sizeof() arguments ahead of treewide
changes, since it needs a manual adjustment for the newly named
sized_strscpy() export.

Cc: Richard Weinberger <richard@nod.at>
Cc: linux-um@lists.infradead.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/um/drivers/net_kern.c               | 2 +-
 arch/um/drivers/vector_kern.c            | 2 +-
 arch/um/drivers/vector_user.c            | 4 ++--
 arch/um/include/shared/user.h            | 2 +-
 arch/um/os-Linux/drivers/ethertap_user.c | 2 +-
 arch/um/os-Linux/drivers/tuntap_user.c   | 2 +-
 arch/um/os-Linux/umid.c                  | 6 +++---
 7 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/um/drivers/net_kern.c b/arch/um/drivers/net_kern.c
index cabcc501b448..77c4afb8ab90 100644
--- a/arch/um/drivers/net_kern.c
+++ b/arch/um/drivers/net_kern.c
@@ -265,7 +265,7 @@ static void uml_net_poll_controller(struct net_device *dev)
 static void uml_net_get_drvinfo(struct net_device *dev,
 				struct ethtool_drvinfo *info)
 {
-	strscpy(info->driver, DRIVER_NAME, sizeof(info->driver));
+	strscpy(info->driver, DRIVER_NAME);
 }
 
 static const struct ethtool_ops uml_net_ethtool_ops = {
diff --git a/arch/um/drivers/vector_kern.c b/arch/um/drivers/vector_kern.c
index 131b7cb29576..dc2feae789cb 100644
--- a/arch/um/drivers/vector_kern.c
+++ b/arch/um/drivers/vector_kern.c
@@ -1373,7 +1373,7 @@ static void vector_net_poll_controller(struct net_device *dev)
 static void vector_net_get_drvinfo(struct net_device *dev,
 				struct ethtool_drvinfo *info)
 {
-	strscpy(info->driver, DRIVER_NAME, sizeof(info->driver));
+	strscpy(info->driver, DRIVER_NAME);
 }
 
 static int vector_net_load_bpf_flash(struct net_device *dev,
diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
index c719e1ec4645..b16a5e5619d3 100644
--- a/arch/um/drivers/vector_user.c
+++ b/arch/um/drivers/vector_user.c
@@ -141,7 +141,7 @@ static int create_tap_fd(char *iface)
 	}
 	memset(&ifr, 0, sizeof(ifr));
 	ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
-	strscpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name));
+	strscpy(ifr.ifr_name, iface);
 
 	err = ioctl(fd, TUNSETIFF, (void *) &ifr);
 	if (err != 0) {
@@ -171,7 +171,7 @@ static int create_raw_fd(char *iface, int flags, int proto)
 		goto raw_fd_cleanup;
 	}
 	memset(&ifr, 0, sizeof(ifr));
-	strscpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name));
+	strscpy(ifr.ifr_name, iface);
 	if (ioctl(fd, SIOCGIFINDEX, (void *) &ifr) < 0) {
 		err = -errno;
 		goto raw_fd_cleanup;
diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
index 9568cc04cbb7..326e52450e41 100644
--- a/arch/um/include/shared/user.h
+++ b/arch/um/include/shared/user.h
@@ -52,7 +52,7 @@ static inline int printk(const char *fmt, ...)
 extern int in_aton(char *str);
 extern size_t strlcat(char *, const char *, size_t);
 extern size_t sized_strscpy(char *, const char *, size_t);
-#define strscpy(dst, src, size)	sized_strscpy(dst, src, size)
+#define strscpy(dst, src)	sized_strscpy(dst, src, sizeof(dst))
 
 /* Copied from linux/compiler-gcc.h since we can't include it directly */
 #define barrier() __asm__ __volatile__("": : :"memory")
diff --git a/arch/um/os-Linux/drivers/ethertap_user.c b/arch/um/os-Linux/drivers/ethertap_user.c
index 3363851a4ae8..bdf215c0eca7 100644
--- a/arch/um/os-Linux/drivers/ethertap_user.c
+++ b/arch/um/os-Linux/drivers/ethertap_user.c
@@ -105,7 +105,7 @@ static int etap_tramp(char *dev, char *gate, int control_me,
 	sprintf(data_fd_buf, "%d", data_remote);
 	sprintf(version_buf, "%d", UML_NET_VERSION);
 	if (gate != NULL) {
-		strscpy(gate_buf, gate, sizeof(gate_buf));
+		strscpy(gate_buf, gate);
 		args = setup_args;
 	}
 	else args = nosetup_args;
diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
index 2284e9c1cbbb..91f0e27ca3a6 100644
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ b/arch/um/os-Linux/drivers/tuntap_user.c
@@ -146,7 +146,7 @@ static int tuntap_open(void *data)
 		}
 		memset(&ifr, 0, sizeof(ifr));
 		ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
-		strscpy(ifr.ifr_name, pri->dev_name, sizeof(ifr.ifr_name));
+		strscpy(ifr.ifr_name, pri->dev_name);
 		if (ioctl(pri->fd, TUNSETIFF, &ifr) < 0) {
 			err = -errno;
 			printk(UM_KERN_ERR "TUNSETIFF failed, errno = %d\n",
diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index 288c422bfa96..e09d65b05d1c 100644
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -40,7 +40,7 @@ static int __init make_uml_dir(void)
 				__func__);
 			goto err;
 		}
-		strscpy(dir, home, sizeof(dir));
+		strscpy(dir, home);
 		uml_dir++;
 	}
 	strlcat(dir, uml_dir, sizeof(dir));
@@ -243,7 +243,7 @@ int __init set_umid(char *name)
 	if (strlen(name) > UMID_LEN - 1)
 		return -E2BIG;
 
-	strscpy(umid, name, sizeof(umid));
+	strscpy(umid, name);
 
 	return 0;
 }
@@ -262,7 +262,7 @@ static int __init make_umid(void)
 	make_uml_dir();
 
 	if (*umid == '\0') {
-		strscpy(tmp, uml_dir, sizeof(tmp));
+		strscpy(tmp, uml_dir);
 		strlcat(tmp, "XXXXXX", sizeof(tmp));
 		fd = mkstemp(tmp);
 		if (fd < 0) {
-- 
2.34.1

Re: [PATCH v2 2/4] string: Allow 2-argument strscpy()

[Geert Uytterhoeven]

Hi Kees,

On Mon, Feb 5, 2024 at 1:37 PM Kees Cook <keescook@chromium.org> wrote:
> Using sizeof(dst) for the "size" argument in strscpy() is the
> overwhelmingly common case. Instead of requiring this everywhere, allow a
> 2-argument version to be used that will use the sizeof() internally. There
> are other functions in the kernel with optional arguments[1], so this
> isn't unprecedented, and improves readability. Update and relocate the
> kern-doc for strscpy() too.
>
> Adjust ARCH=um build to notice the changed export name, as it doesn't
> do full header includes for the string helpers.
>
> This could additionally let us save a few hundred lines of code:
>  1177 files changed, 2455 insertions(+), 3026 deletions(-)
> with a treewide cleanup using Coccinelle:
>
> @needless_arg@
> expression DST, SRC;
> @@
>
>         strscpy(DST, SRC
> -, sizeof(DST)
>         )
>
> Link: https://elixir.bootlin.com/linux/v6.7/source/include/linux/pci.h#L1517 [1]
> Reviewed-by: Justin Stitt <justinstitt@google.com>
> Cc: Andy Shevchenko <andy@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks for your patch!

> --- a/include/linux/string.h
> +++ b/include/linux/string.h

> +/*
> + * The 2 argument style can only be used when dst is an array with a
> + * known size.
> + */
> +#define __strscpy0(dst, src, ...)      \
> +       sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
> +#define __strscpy1(dst, src, size)     sized_strscpy(dst, src, size)

(dst), (src), (size) etc.


> +
> +/**
> + * strscpy - Copy a C-string into a sized buffer
> + * @dst: Where to copy the string to
> + * @src: Where to copy the string from
> + * @...: Size of destination buffer (optional)
> + *
> + * Copy the source string @src, or as much of it as fits, into the
> + * destination @dst buffer. The behavior is undefined if the string
> + * buffers overlap. The destination @dst buffer is always NUL terminated,
> + * unless it's zero-sized.
> + *
> + * The size argument @... is only required when @dst is not an array, or
> + * when the copy needs to be smaller than sizeof(@dst).
> + *
> + * Preferred to strncpy() since it always returns a valid string, and
> + * doesn't unnecessarily force the tail of the destination buffer to be
> + * zero padded. If padding is desired please use strscpy_pad().
> + *
> + * Returns the number of characters copied in @dst (not including the
> + * trailing %NUL) or -E2BIG if @size is 0 or the copy from @src was
> + * truncated.
> + */
> +#define strscpy(dst, src, ...) \
> +       CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)

Likewise

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v2 3/4] string: Allow 2-argument strscpy_pad()

[Geert Uytterhoeven]

Hi Kees,

On Mon, Feb 5, 2024 at 1:36 PM Kees Cook <keescook@chromium.org> wrote:
> Similar to strscpy(), update strscpy_pad()'s 3rd argument to be
> optional when the destination is a compile-time known size array.
>
> Cc: Andy Shevchenko <andy@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks for your patch!

> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -78,6 +78,10 @@ ssize_t sized_strscpy(char *, const char *, size_t);
>         sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
>  #define __strscpy1(dst, src, size)     sized_strscpy(dst, src, size)
>
> +#define __strscpy_pad0(dst, src, ...)  \
> +       sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst))
> +#define __strscpy_pad1(dst, src, size) sized_strscpy_pad(dst, src, size)

(dst) etc.

> @@ -123,17 +139,8 @@ ssize_t sized_strscpy(char *, const char *, size_t);
>   * * The number of characters copied (not including the trailing %NULs)
>   * * -E2BIG if count is 0 or @src was truncated.
>   */
> -#define strscpy_pad(dest, src, count)  ({                      \
> -       char *__dst = (dest);                                           \
> -       const char *__src = (src);                                      \
> -       const size_t __count = (count);                                 \
> -       ssize_t __wrote;                                                \
> -                                                                       \
> -       __wrote = strscpy(__dst, __src, __count);                       \
> -       if (__wrote >= 0 && __wrote < __count)                          \
> -               memset(__dst + __wrote + 1, 0, __count - __wrote - 1);  \
> -       __wrote;                                                        \
> -})
> +#define strscpy_pad(dst, src, ...)     \
> +       CONCATENATE(__strscpy_pad, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)

Likewise,

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v2 4/4] um: Convert strscpy() usage to 2-argument style

[Geert Uytterhoeven]

Hi Kees,

On Mon, Feb 5, 2024 at 1:36 PM Kees Cook <keescook@chromium.org> wrote:
> The ARCH=um build has its own idea about strscpy()'s definition. Adjust
> the callers to remove the redundant sizeof() arguments ahead of treewide
> changes, since it needs a manual adjustment for the newly named
> sized_strscpy() export.
>
> Cc: Richard Weinberger <richard@nod.at>
> Cc: linux-um@lists.infradead.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks for your patch!

> --- a/arch/um/include/shared/user.h
> +++ b/arch/um/include/shared/user.h
> @@ -52,7 +52,7 @@ static inline int printk(const char *fmt, ...)
>  extern int in_aton(char *str);
>  extern size_t strlcat(char *, const char *, size_t);
>  extern size_t sized_strscpy(char *, const char *, size_t);
> -#define strscpy(dst, src, size)        sized_strscpy(dst, src, size)
> +#define strscpy(dst, src)      sized_strscpy(dst, src, sizeof(dst))

(dst), (src)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v2 3/4] string: Allow 2-argument strscpy_pad()

[Andy Shevchenko]

On Mon, Feb 05, 2024 at 01:48:51PM +0100, Geert Uytterhoeven wrote:
> On Mon, Feb 5, 2024 at 1:36 PM Kees Cook <keescook@chromium.org> wrote:

...

> > +#define __strscpy_pad1(dst, src, size) sized_strscpy_pad(dst, src, size)
> 
> (dst) etc.

Makes a little sense here. Are you expecting, e.g., dst to be 'a, b' (w/o
quotes where a and b are expressions)?

...

> > +#define strscpy_pad(dst, src, ...)     \
> > +       CONCATENATE(__strscpy_pad, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
> 
> Likewise,

Ditto.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 4/4] um: Convert strscpy() usage to 2-argument style

[Andy Shevchenko]

On Mon, Feb 05, 2024 at 01:50:14PM +0100, Geert Uytterhoeven wrote:
> On Mon, Feb 5, 2024 at 1:36 PM Kees Cook <keescook@chromium.org> wrote:

...

> > +#define strscpy(dst, src)      sized_strscpy(dst, src, sizeof(dst))
> 
> (dst), (src)

No need.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 2/4] string: Allow 2-argument strscpy()

[Andy Shevchenko]

On Mon, Feb 05, 2024 at 01:47:08PM +0100, Geert Uytterhoeven wrote:
> On Mon, Feb 5, 2024 at 1:37 PM Kees Cook <keescook@chromium.org> wrote:

...

> > +#define __strscpy1(dst, src, size)     sized_strscpy(dst, src, size)
> 
> (dst), (src), (size) etc.

No need.

...

> > +#define strscpy(dst, src, ...) \
> > +       CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
> 
> Likewise

Likewise

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 2/4] string: Allow 2-argument strscpy()

[Kees Cook]

On Mon, Feb 05, 2024 at 01:47:08PM +0100, Geert Uytterhoeven wrote:
> > +/*
> > + * The 2 argument style can only be used when dst is an array with a
> > + * known size.
> > + */
> > +#define __strscpy0(dst, src, ...)      \
> > +       sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
> > +#define __strscpy1(dst, src, size)     sized_strscpy(dst, src, size)
> 
> (dst), (src), (size) etc.

I normally don't do this when macro args are being expanded into
function arguments. I've only done it for when macro args are used in
expressions. Am I missing a side-effect here, or is this more about
stylistic consistency?

-- 
Kees Cook

Re: [PATCH v2 2/4] string: Allow 2-argument strscpy()

[Geert Uytterhoeven]

Hi Kees,

On Mon, Feb 5, 2024 at 2:01 PM Kees Cook <keescook@chromium.org> wrote:
> On Mon, Feb 05, 2024 at 01:47:08PM +0100, Geert Uytterhoeven wrote:
> > > +/*
> > > + * The 2 argument style can only be used when dst is an array with a
> > > + * known size.
> > > + */
> > > +#define __strscpy0(dst, src, ...)      \
> > > +       sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
> > > +#define __strscpy1(dst, src, size)     sized_strscpy(dst, src, size)
> >
> > (dst), (src), (size) etc.
>
> I normally don't do this when macro args are being expanded into
> function arguments. I've only done it for when macro args are used in
> expressions. Am I missing a side-effect here, or is this more about
> stylistic consistency?

I'm not 100% sure it is needed, but I'm always wary when using macro
parameters without parentheses, except in the most simple use-cases.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds