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Message-Id: <20240206142221.2208763-2-keescook@chromium.org>
Date: Tue, 6 Feb 2024 06:22:17 -0800
From: Kees Cook <keescook@...omium.org>
To: Andy Shevchenko <andy@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
Justin Stitt <justinstitt@...gle.com>,
linux-hardening@...r.kernel.org,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Johannes Berg <johannes@...solutions.net>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
Jason Wang <jasowang@...hat.com>,
kernel test robot <lkp@...el.com>,
Nathan Chancellor <nathan@...nel.org>,
Azeem Shaikh <azeemshaikh38@...il.com>,
linux-kernel@...r.kernel.org,
linux-um@...ts.infradead.org
Subject: [PATCH v3 2/4] string: Allow 2-argument strscpy()
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@...gle.com>
Cc: Andy Shevchenko <andy@...nel.org>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
arch/um/include/shared/user.h | 3 ++-
include/linux/fortify-string.h | 22 ++-------------------
include/linux/string.h | 36 +++++++++++++++++++++++++++++++++-
lib/string.c | 4 ++--
4 files changed, 41 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..79b875de615e 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -2,6 +2,7 @@
#ifndef _LINUX_STRING_H_
#define _LINUX_STRING_H_
+#include <linux/args.h>
#include <linux/array_size.h>
#include <linux/compiler.h> /* for inline */
#include <linux/types.h> /* for size_t */
@@ -67,9 +68,42 @@ 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
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