From: tobin at kernel.org (Tobin C. Harding) Subject: [PATCH v3 6/7] lib/string: Add strscpy_pad() function Date: Thu, 7 Mar 2019 08:42:25 +1100 [thread overview] Message-ID: <20190306214226.14598-7-tobin@kernel.org> (raw) In-Reply-To: <20190306214226.14598-1-tobin@kernel.org> We have a function to copy strings safely and we have a function to copy strings and zero the tail of the destination (if source string is shorter than destination buffer) but we do not have a function to do both at once. This means developers must write this themselves if they desire this functionality. This is a chore, and also leaves us open to off by one errors unnecessarily. Add a function that calls strscpy() then memset()s the tail to zero if the source string is shorter than the destination buffer. Signed-off-by: Tobin C. Harding <tobin at kernel.org> --- include/linux/string.h | 4 ++++ lib/string.c | 47 +++++++++++++++++++++++++++++++++++------- 2 files changed, 44 insertions(+), 7 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index 7927b875f80c..bfe95bf5d07e 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -31,6 +31,10 @@ size_t strlcpy(char *, const char *, size_t); #ifndef __HAVE_ARCH_STRSCPY 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); + #ifndef __HAVE_ARCH_STRCAT extern char * strcat(char *, const char *); #endif diff --git a/lib/string.c b/lib/string.c index 38e4ca08e757..3a3353512184 100644 --- a/lib/string.c +++ b/lib/string.c @@ -159,11 +159,9 @@ EXPORT_SYMBOL(strlcpy); * @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 routine returns the number of characters copied (not including - * the trailing NUL) or -E2BIG if the destination buffer wasn't big enough. - * The behavior is undefined if the string buffers overlap. - * The destination buffer is always NUL terminated, unless it's zero-sized. + * 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. * * Preferred to strlcpy() since the API doesn't require reading memory * from the src string beyond the specified "count" bytes, and since @@ -173,8 +171,10 @@ EXPORT_SYMBOL(strlcpy); * * Preferred to strncpy() since it always returns a valid string, and * doesn't unnecessarily force the tail of the destination buffer to be - * zeroed. If the zeroing is desired, it's likely cleaner to use strscpy() - * with an overflow test, then just memset() the tail of the dest buffer. + * zeroed. If zeroing is desired please use strscpy_pad(). + * + * Return: The number of characters copied (not including the trailing + * %NUL) or -E2BIG if the destination buffer wasn't big enough. */ ssize_t strscpy(char *dest, const char *src, size_t count) { @@ -237,6 +237,39 @@ ssize_t strscpy(char *dest, const char *src, size_t count) EXPORT_SYMBOL(strscpy); #endif +/** + * 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(). + * + * Return: The number of characters copied (not including the trailing + * %NUL) or -E2BIG if the destination buffer wasn't big enough. + */ +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); + #ifndef __HAVE_ARCH_STRCAT /** * strcat - Append one %NUL-terminated string to another -- 2.20.1
WARNING: multiple messages have this Message-ID (diff)
From: tobin@kernel.org (Tobin C. Harding) Subject: [PATCH v3 6/7] lib/string: Add strscpy_pad() function Date: Thu, 7 Mar 2019 08:42:25 +1100 [thread overview] Message-ID: <20190306214226.14598-7-tobin@kernel.org> (raw) Message-ID: <20190306214225.R1JvwESZxkPCnfG5Sehmc_1rZlGIaVs0F-pxI298-Pg@z> (raw) In-Reply-To: <20190306214226.14598-1-tobin@kernel.org> We have a function to copy strings safely and we have a function to copy strings and zero the tail of the destination (if source string is shorter than destination buffer) but we do not have a function to do both at once. This means developers must write this themselves if they desire this functionality. This is a chore, and also leaves us open to off by one errors unnecessarily. Add a function that calls strscpy() then memset()s the tail to zero if the source string is shorter than the destination buffer. Signed-off-by: Tobin C. Harding <tobin at kernel.org> --- include/linux/string.h | 4 ++++ lib/string.c | 47 +++++++++++++++++++++++++++++++++++------- 2 files changed, 44 insertions(+), 7 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index 7927b875f80c..bfe95bf5d07e 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -31,6 +31,10 @@ size_t strlcpy(char *, const char *, size_t); #ifndef __HAVE_ARCH_STRSCPY 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); + #ifndef __HAVE_ARCH_STRCAT extern char * strcat(char *, const char *); #endif diff --git a/lib/string.c b/lib/string.c index 38e4ca08e757..3a3353512184 100644 --- a/lib/string.c +++ b/lib/string.c @@ -159,11 +159,9 @@ EXPORT_SYMBOL(strlcpy); * @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 routine returns the number of characters copied (not including - * the trailing NUL) or -E2BIG if the destination buffer wasn't big enough. - * The behavior is undefined if the string buffers overlap. - * The destination buffer is always NUL terminated, unless it's zero-sized. + * 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. * * Preferred to strlcpy() since the API doesn't require reading memory * from the src string beyond the specified "count" bytes, and since @@ -173,8 +171,10 @@ EXPORT_SYMBOL(strlcpy); * * Preferred to strncpy() since it always returns a valid string, and * doesn't unnecessarily force the tail of the destination buffer to be - * zeroed. If the zeroing is desired, it's likely cleaner to use strscpy() - * with an overflow test, then just memset() the tail of the dest buffer. + * zeroed. If zeroing is desired please use strscpy_pad(). + * + * Return: The number of characters copied (not including the trailing + * %NUL) or -E2BIG if the destination buffer wasn't big enough. */ ssize_t strscpy(char *dest, const char *src, size_t count) { @@ -237,6 +237,39 @@ ssize_t strscpy(char *dest, const char *src, size_t count) EXPORT_SYMBOL(strscpy); #endif +/** + * 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(). + * + * Return: The number of characters copied (not including the trailing + * %NUL) or -E2BIG if the destination buffer wasn't big enough. + */ +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); + #ifndef __HAVE_ARCH_STRCAT /** * strcat - Append one %NUL-terminated string to another -- 2.20.1
next prev parent reply other threads:[~2019-03-06 21:42 UTC|newest] Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-03-06 21:42 [PATCH v3 0/7] lib/string: Add strscpy_pad() function tobin 2019-03-06 21:42 ` Tobin C. Harding 2019-03-06 21:42 ` [PATCH v3 1/7] lib/test_printf: Add empty module_exit function tobin 2019-03-06 21:42 ` Tobin C. Harding 2019-04-02 21:24 ` keescook 2019-04-02 21:24 ` Kees Cook 2019-03-06 21:42 ` [PATCH v3 2/7] kselftest: Add test runner creation script tobin 2019-03-06 21:42 ` Tobin C. Harding 2019-04-02 21:27 ` keescook 2019-04-02 21:27 ` Kees Cook 2019-04-02 21:33 ` rdunlap 2019-04-02 21:33 ` Randy Dunlap 2019-04-04 23:16 ` me 2019-04-04 23:16 ` Tobin C. Harding 2019-03-06 21:42 ` [PATCH v3 3/7] kselftest/lib: Use new shell runner to define tests tobin 2019-03-06 21:42 ` Tobin C. Harding 2019-04-02 21:29 ` keescook 2019-04-02 21:29 ` Kees Cook 2019-04-02 21:45 ` keescook 2019-04-02 21:45 ` Kees Cook 2019-04-02 21:51 ` keescook 2019-04-02 21:51 ` Kees Cook 2019-03-06 21:42 ` [PATCH v3 4/7] kselftest: Add test module framework header tobin 2019-03-06 21:42 ` Tobin C. Harding 2019-04-02 21:31 ` keescook 2019-04-02 21:31 ` Kees Cook 2019-03-06 21:42 ` [PATCH v3 5/7] lib: Use new kselftest header tobin 2019-03-06 21:42 ` Tobin C. Harding 2019-04-02 21:32 ` keescook 2019-04-02 21:32 ` Kees Cook 2019-03-06 21:42 ` tobin [this message] 2019-03-06 21:42 ` [PATCH v3 6/7] lib/string: Add strscpy_pad() function Tobin C. Harding 2019-04-02 21:35 ` keescook 2019-04-02 21:35 ` Kees Cook 2019-03-06 21:42 ` [PATCH v3 7/7] lib: Add test module for strscpy_pad tobin 2019-03-06 21:42 ` Tobin C. Harding 2019-04-02 21:36 ` keescook 2019-04-02 21:36 ` Kees Cook 2019-03-06 21:49 ` [PATCH v3 0/7] lib/string: Add strscpy_pad() function me 2019-03-06 21:49 ` Tobin C. Harding 2019-03-07 21:18 ` me 2019-03-07 21:18 ` Tobin C. Harding 2019-03-07 22:43 ` keescook 2019-03-07 22:43 ` Kees Cook 2019-03-08 5:23 ` me 2019-03-08 5:23 ` Tobin C. Harding 2019-03-08 16:18 ` keescook 2019-03-08 16:18 ` Kees Cook 2019-04-02 21:37 ` keescook 2019-04-02 21:37 ` Kees Cook 2019-04-03 0:25 ` me 2019-04-03 0:25 ` Tobin C. Harding 2019-04-03 0:29 ` shuah 2019-04-03 0:29 ` shuah
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