From 30035e45753b708e7d47a98398500ca005e02b86 Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Wed, 29 Apr 2015 12:52:04 -0400 Subject: string: provide strscpy() The strscpy() API is intended to be used instead of strlcpy(), and instead of most uses of strncpy(). - Unlike strlcpy(), it doesn't read from memory beyond (src + size). - Unlike strlcpy() or strncpy(), the API provides an easy way to check for destination buffer overflow: an -E2BIG error return value. - The provided implementation is robust in the face of the source buffer being asynchronously changed during the copy, unlike the current implementation of strlcpy(). - Unlike strncpy(), the destination buffer will be NUL-terminated if the string in the source buffer is too long. - Also unlike strncpy(), the destination buffer will not be updated beyond the NUL termination, avoiding strncpy's behavior of zeroing the entire tail end of the destination buffer. (A memset() after the strscpy() can be used if this behavior is desired.) - The implementation should be reasonably performant on all platforms since it uses the asm/word-at-a-time.h API rather than simple byte copy. Kernel-to-kernel string copy is not considered to be performance critical in any case. Signed-off-by: Chris Metcalf --- lib/string.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) (limited to 'lib') diff --git a/lib/string.c b/lib/string.c index 13d1e84ddb80..8dbb7b1eab50 100644 --- a/lib/string.c +++ b/lib/string.c @@ -27,6 +27,10 @@ #include #include +#include +#include +#include + #ifndef __HAVE_ARCH_STRNCASECMP /** * strncasecmp - Case insensitive, length-limited string comparison @@ -146,6 +150,90 @@ size_t strlcpy(char *dest, const char *src, size_t size) EXPORT_SYMBOL(strlcpy); #endif +#ifndef __HAVE_ARCH_STRSCPY +/** + * strscpy - 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 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. + * + * Preferred to strlcpy() since the API doesn't require reading memory + * from the src string beyond the specified "count" bytes, and since + * the return value is easier to error-check than strlcpy()'s. + * In addition, the implementation is robust to the string changing out + * from underneath it, unlike the current strlcpy() implementation. + * + * 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. + */ +ssize_t 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; + long res = 0; + + if (count == 0) + return -E2BIG; + +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS + /* + * If src is unaligned, don't cross a page boundary, + * since we don't know if the next page is mapped. + */ + if ((long)src & (sizeof(long) - 1)) { + size_t limit = PAGE_SIZE - ((long)src & (PAGE_SIZE - 1)); + if (limit < max) + max = limit; + } +#else + /* If src or dest is unaligned, don't do word-at-a-time. */ + if (((long) dest | (long) src) & (sizeof(long) - 1)) + max = 0; +#endif + + while (max >= sizeof(unsigned long)) { + unsigned long c, data; + + c = *(unsigned long *)(src+res); + *(unsigned long *)(dest+res) = c; + if (has_zero(c, &data, &constants)) { + data = prep_zero_mask(c, data, &constants); + data = create_zero_mask(data); + return res + find_zero(data); + } + res += sizeof(unsigned long); + count -= sizeof(unsigned long); + max -= sizeof(unsigned long); + } + + while (count) { + char c; + + c = src[res]; + dest[res] = c; + if (!c) + return res; + res++; + count--; + } + + /* Hit buffer length without finding a NUL; force NUL-termination. */ + if (res) + dest[res-1] = '\0'; + + return -E2BIG; +} +EXPORT_SYMBOL(strscpy); +#endif + #ifndef __HAVE_ARCH_STRCAT /** * strcat - Append one %NUL-terminated string to another -- cgit v1.2.3 From 990486c8af044f89bddfbde1d1cf9fde449bedbf Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Tue, 6 Oct 2015 12:37:41 -0400 Subject: strscpy: zero any trailing garbage bytes in the destination It's possible that the destination can be shadowed in userspace (as, for example, the perf buffers are now). So we should take care not to leak data that could be inspected by userspace. Signed-off-by: Chris Metcalf --- lib/string.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'lib') diff --git a/lib/string.c b/lib/string.c index 8dbb7b1eab50..84775ba873b9 100644 --- a/lib/string.c +++ b/lib/string.c @@ -203,12 +203,13 @@ ssize_t strscpy(char *dest, const char *src, size_t count) unsigned long c, data; c = *(unsigned long *)(src+res); - *(unsigned long *)(dest+res) = c; if (has_zero(c, &data, &constants)) { data = prep_zero_mask(c, data, &constants); data = create_zero_mask(data); + *(unsigned long *)(dest+res) = c & zero_bytemask(data); return res + find_zero(data); } + *(unsigned long *)(dest+res) = c; res += sizeof(unsigned long); count -= sizeof(unsigned long); max -= sizeof(unsigned long); -- cgit v1.2.3 From 1fd4e5c347bfcef6ae2c31f6a2abce00f6ecaa3f Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Thu, 15 Oct 2015 15:28:35 -0700 Subject: lib/Kconfig: ZLIB_DEFLATE must select BITREVERSE lib/built-in.o: In function `__bitrev32': deftree.c:(.text+0x1e799): undefined reference to `byte_rev_table' deftree.c:(.text+0x1e7a0): undefined reference to `byte_rev_table' deftree.c:(.text+0x1e7b4): undefined reference to `byte_rev_table' deftree.c:(.text+0x1e7c1): undefined reference to `byte_rev_table' Anything which uses bitrevX() has to select BITREVERSE, to grab lib/bitrev.o. Reported-by: Jim Davis Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/Kconfig | 1 + 1 file changed, 1 insertion(+) (limited to 'lib') diff --git a/lib/Kconfig b/lib/Kconfig index 2e491ac15622..f0df318104e7 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -220,6 +220,7 @@ config ZLIB_INFLATE config ZLIB_DEFLATE tristate + select BITREVERSE config LZO_COMPRESS tristate -- cgit v1.2.3