diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Kconfig | 3 | ||||
| -rw-r--r-- | lib/Makefile | 2 | ||||
| -rw-r--r-- | lib/strncpy_from_user.c | 146 |
3 files changed, 151 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig index 4a8aba2e5cc0..49cb46337db9 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -16,6 +16,9 @@ config BITREVERSE config RATIONAL boolean +config GENERIC_STRNCPY_FROM_USER + bool + config GENERIC_FIND_FIRST_BIT bool diff --git a/lib/Makefile b/lib/Makefile index 18515f0267c4..57538b4d01d2 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -123,6 +123,8 @@ obj-$(CONFIG_SIGNATURE) += digsig.o obj-$(CONFIG_CLZ_TAB) += clz_tab.o +obj-$(CONFIG_GENERIC_STRNCPY_FROM_USER) += strncpy_from_user.o + hostprogs-y := gen_crc32table clean-files := crc32table.h diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c new file mode 100644 index 000000000000..c4c09b0e96ba --- /dev/null +++ b/lib/strncpy_from_user.c @@ -0,0 +1,146 @@ +#include <linux/module.h> +#include <linux/uaccess.h> +#include <linux/kernel.h> +#include <linux/errno.h> + +#include <asm/byteorder.h> + +static inline long find_zero(unsigned long mask) +{ + long byte = 0; + +#ifdef __BIG_ENDIAN +#ifdef CONFIG_64BIT + if (mask >> 32) + mask >>= 32; + else + byte = 4; +#endif + if (mask >> 16) + mask >>= 16; + else + byte += 2; + return (mask >> 8) ? byte : byte + 1; +#else +#ifdef CONFIG_64BIT + if (!((unsigned int) mask)) { + mask >>= 32; + byte = 4; + } +#endif + if (!(mask & 0xffff)) { + mask >>= 16; + byte += 2; + } + return (mask & 0xff) ? byte : byte + 1; +#endif +} + +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS +#define IS_UNALIGNED(src, dst) 0 +#else +#define IS_UNALIGNED(src, dst) \ + (((long) dst | (long) src) & (sizeof(long) - 1)) +#endif + +/* + * Do a strncpy, return length of string without final '\0'. + * 'count' is the user-supplied count (return 'count' if we + * hit it), 'max' is the address space maximum (and we return + * -EFAULT if we hit it). + */ +static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max) +{ + const unsigned long high_bits = REPEAT_BYTE(0xfe) + 1; + const unsigned long low_bits = REPEAT_BYTE(0x7f); + long res = 0; + + /* + * Truncate 'max' to the user-specified limit, so that + * we only have one limit we need to check in the loop + */ + if (max > count) + max = count; + + if (IS_UNALIGNED(src, dst)) + goto byte_at_a_time; + + while (max >= sizeof(unsigned long)) { + unsigned long c, v, rhs; + + /* Fall back to byte-at-a-time if we get a page fault */ + if (unlikely(__get_user(c,(unsigned long __user *)(src+res)))) + break; + rhs = c | low_bits; + v = (c + high_bits) & ~rhs; + *(unsigned long *)(dst+res) = c; + if (v) { + v = (c & low_bits) + low_bits; + v = ~(v | rhs); + return res + find_zero(v); + } + res += sizeof(unsigned long); + max -= sizeof(unsigned long); + } + +byte_at_a_time: + while (max) { + char c; + + if (unlikely(__get_user(c,src+res))) + return -EFAULT; + dst[res] = c; + if (!c) + return res; + res++; + max--; + } + + /* + * Uhhuh. We hit 'max'. But was that the user-specified maximum + * too? If so, that's ok - we got as much as the user asked for. + */ + if (res >= count) + return res; + + /* + * Nope: we hit the address space limit, and we still had more + * characters the caller would have wanted. That's an EFAULT. + */ + return -EFAULT; +} + +/** + * strncpy_from_user: - Copy a NUL terminated string from userspace. + * @dst: Destination address, in kernel space. This buffer must be at + * least @count bytes long. + * @src: Source address, in user space. + * @count: Maximum number of bytes to copy, including the trailing NUL. + * + * Copies a NUL-terminated string from userspace to kernel space. + * + * On success, returns the length of the string (not including the trailing + * NUL). + * + * If access to userspace fails, returns -EFAULT (some data may have been + * copied). + * + * If @count is smaller than the length of the string, copies @count bytes + * and returns @count. + */ +long strncpy_from_user(char *dst, const char __user *src, long count) +{ + unsigned long max_addr, src_addr; + + if (unlikely(count <= 0)) + return 0; + + max_addr = user_addr_max(); + src_addr = (unsigned long)src; + if (likely(src_addr < max_addr)) { + unsigned long max = max_addr - src_addr; + return do_strncpy_from_user(dst, src, count, max); + } + return -EFAULT; +} +EXPORT_SYMBOL(strncpy_from_user); |