#include <linux/kernel.h> #include <linux/export.h> #include <linux/uaccess.h> #include <asm/word-at-a-time.h> /* Set bits in the first 'n' bytes when loaded from memory */ #ifdef __LITTLE_ENDIAN # define aligned_byte_mask(n) ((1ul << 8*(n))-1) #else # define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n))) #endif /* * Do a strnlen, return length of string *with* final '\0'. * 'count' is the user-supplied count, while 'max' is the * address space maximum. * * Return 0 for exceptions (which includes hitting the address * space maximum), or 'count+1' if hitting the user-supplied * maximum count. * * NOTE! We can sometimes overshoot the user-supplied maximum * if it fits in a aligned 'long'. The caller needs to check * the return value against "> max". */ static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) { const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; long align, res = 0; unsigned long c; /* * 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; /* * Do everything aligned. But that means that we * need to also expand the maximum.. */ align = (sizeof(long) - 1) & (unsigned long)src; src -= align; max += align; if (unlikely(unsafe_get_user(c,(unsigned long __user *)src))) return 0; c |= aligned_byte_mask(align); for (;;) { unsigned long data; if (has_zero(c, &data, &constants)) { data = prep_zero_mask(c, data, &constants); data = create_zero_mask(data); return res + find_zero(data) + 1 - align; } res += sizeof(unsigned long); /* We already handled 'unsigned long' bytes. Did we do it all ? */ if (unlikely(max <= sizeof(unsigned long))) break; max -= sizeof(unsigned long); if (unlikely(unsafe_get_user(c,(unsigned long __user *)(src+res)))) return 0; } res -= align; /* * Uhhuh. We hit 'max'. But was that the user-specified maximum * too? If so, return the marker for "too long". */ if (res >= count) return count+1; /* * Nope: we hit the address space limit, and we still had more * characters the caller would have wanted. That's 0. */ return 0; } /** * strnlen_user: - Get the size of a user string INCLUDING final NUL. * @str: The string to measure. * @count: Maximum count (including NUL character) * * Context: User context only. This function may sleep if pagefaults are * enabled. * * Get the size of a NUL-terminated string in user space. * * Returns the size of the string INCLUDING the terminating NUL. * If the string is too long, returns a number larger than @count. User * has to check the return value against "> count". * On exception (or invalid count), returns 0. * * NOTE! You should basically never use this function. There is * almost never any valid case for using the length of a user space * string, since the string can be changed at any time by other * threads. Use "strncpy_from_user()" instead to get a stable copy * of the string. */ long strnlen_user(const char __user *str, long count) { unsigned long max_addr, src_addr; if (unlikely(count <= 0)) return 0; max_addr = user_addr_max(); src_addr = (unsigned long)str; if (likely(src_addr < max_addr)) { unsigned long max = max_addr - src_addr; long retval; user_access_begin(); retval = do_strnlen_user(str, count, max); user_access_end(); return retval; } return 0; } EXPORT_SYMBOL(strnlen_user); /** * strlen_user: - Get the size of a user string INCLUDING final NUL. * @str: The string to measure. * * Context: User context only. This function may sleep if pagefaults are * enabled. * * Get the size of a NUL-terminated string in user space. * * Returns the size of the string INCLUDING the terminating NUL. * On exception, returns 0. * * If there is a limit on the length of a valid string, you may wish to * consider using strnlen_user() instead. */ long strlen_user(const char __user *str) { unsigned long max_addr, src_addr; max_addr = user_addr_max(); src_addr = (unsigned long)str; if (likely(src_addr < max_addr)) { unsigned long max = max_addr - src_addr; long retval; user_access_begin(); retval = do_strnlen_user(str, ~0ul, max); user_access_end(); return retval; } return 0; } EXPORT_SYMBOL(strlen_user);