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#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/errno.h>
#include <linux/bug.h>
void copy_from_user_overflow(void)
{
WARN(1, "Buffer overflow detected!\n");
}
EXPORT_SYMBOL(copy_from_user_overflow);
#define REPEAT_BYTE(x) ((~0ul / 0xff) * (x))
/* Return the high bit set in the first byte that is a zero */
static inline unsigned long has_zero(unsigned long a)
{
return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
}
static inline long find_zero(unsigned long c)
{
#ifdef CONFIG_64BIT
if (!(c & 0xff00000000000000UL))
return 0;
if (!(c & 0x00ff000000000000UL))
return 1;
if (!(c & 0x0000ff0000000000UL))
return 2;
if (!(c & 0x000000ff00000000UL))
return 3;
#define __OFF 4
#else
#define __OFF 0
#endif
if (!(c & 0xff000000))
return __OFF + 0;
if (!(c & 0x00ff0000))
return __OFF + 1;
if (!(c & 0x0000ff00))
return __OFF + 2;
return __OFF + 3;
#undef __OFF
}
/*
* 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)
{
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 (((long) dst | (long) src) & (sizeof(long) - 1))
goto byte_at_a_time;
while (max >= sizeof(unsigned long)) {
unsigned long c;
/* Fall back to byte-at-a-time if we get a page fault */
if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
break;
*(unsigned long *)(dst+res) = c;
if (has_zero(c))
return res + find_zero(c);
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 = ~0UL;
if (likely(segment_eq(get_fs(), USER_DS)))
max_addr = STACK_TOP;
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);
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