1 #include <linux/kernel.h> 2 #include <linux/export.h> 3 #include <linux/uaccess.h> 4 5 #include <asm/word-at-a-time.h> 6 7 /* Set bits in the first 'n' bytes when loaded from memory */ 8 #ifdef __LITTLE_ENDIAN 9 # define aligned_byte_mask(n) ((1ul << 8*(n))-1) 10 #else 11 # define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n))) 12 #endif 13 14 /* 15 * Do a strnlen, return length of string *with* final '\0'. 16 * 'count' is the user-supplied count, while 'max' is the 17 * address space maximum. 18 * 19 * Return 0 for exceptions (which includes hitting the address 20 * space maximum), or 'count+1' if hitting the user-supplied 21 * maximum count. 22 * 23 * NOTE! We can sometimes overshoot the user-supplied maximum 24 * if it fits in a aligned 'long'. The caller needs to check 25 * the return value against "> max". 26 */ 27 static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) 28 { 29 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; 30 long align, res = 0; 31 unsigned long c; 32 33 /* 34 * Truncate 'max' to the user-specified limit, so that 35 * we only have one limit we need to check in the loop 36 */ 37 if (max > count) 38 max = count; 39 40 /* 41 * Do everything aligned. But that means that we 42 * need to also expand the maximum.. 43 */ 44 align = (sizeof(long) - 1) & (unsigned long)src; 45 src -= align; 46 max += align; 47 48 unsafe_get_user(c, (unsigned long __user *)src, efault); 49 c |= aligned_byte_mask(align); 50 51 for (;;) { 52 unsigned long data; 53 if (has_zero(c, &data, &constants)) { 54 data = prep_zero_mask(c, data, &constants); 55 data = create_zero_mask(data); 56 return res + find_zero(data) + 1 - align; 57 } 58 res += sizeof(unsigned long); 59 /* We already handled 'unsigned long' bytes. Did we do it all ? */ 60 if (unlikely(max <= sizeof(unsigned long))) 61 break; 62 max -= sizeof(unsigned long); 63 unsafe_get_user(c, (unsigned long __user *)(src+res), efault); 64 } 65 res -= align; 66 67 /* 68 * Uhhuh. We hit 'max'. But was that the user-specified maximum 69 * too? If so, return the marker for "too long". 70 */ 71 if (res >= count) 72 return count+1; 73 74 /* 75 * Nope: we hit the address space limit, and we still had more 76 * characters the caller would have wanted. That's 0. 77 */ 78 efault: 79 return 0; 80 } 81 82 /** 83 * strnlen_user: - Get the size of a user string INCLUDING final NUL. 84 * @str: The string to measure. 85 * @count: Maximum count (including NUL character) 86 * 87 * Context: User context only. This function may sleep if pagefaults are 88 * enabled. 89 * 90 * Get the size of a NUL-terminated string in user space. 91 * 92 * Returns the size of the string INCLUDING the terminating NUL. 93 * If the string is too long, returns a number larger than @count. User 94 * has to check the return value against "> count". 95 * On exception (or invalid count), returns 0. 96 * 97 * NOTE! You should basically never use this function. There is 98 * almost never any valid case for using the length of a user space 99 * string, since the string can be changed at any time by other 100 * threads. Use "strncpy_from_user()" instead to get a stable copy 101 * of the string. 102 */ 103 long strnlen_user(const char __user *str, long count) 104 { 105 unsigned long max_addr, src_addr; 106 107 if (unlikely(count <= 0)) 108 return 0; 109 110 max_addr = user_addr_max(); 111 src_addr = (unsigned long)str; 112 if (likely(src_addr < max_addr)) { 113 unsigned long max = max_addr - src_addr; 114 long retval; 115 116 user_access_begin(); 117 retval = do_strnlen_user(str, count, max); 118 user_access_end(); 119 return retval; 120 } 121 return 0; 122 } 123 EXPORT_SYMBOL(strnlen_user); 124 125 /** 126 * strlen_user: - Get the size of a user string INCLUDING final NUL. 127 * @str: The string to measure. 128 * 129 * Context: User context only. This function may sleep if pagefaults are 130 * enabled. 131 * 132 * Get the size of a NUL-terminated string in user space. 133 * 134 * Returns the size of the string INCLUDING the terminating NUL. 135 * On exception, returns 0. 136 * 137 * If there is a limit on the length of a valid string, you may wish to 138 * consider using strnlen_user() instead. 139 */ 140 long strlen_user(const char __user *str) 141 { 142 unsigned long max_addr, src_addr; 143 144 max_addr = user_addr_max(); 145 src_addr = (unsigned long)str; 146 if (likely(src_addr < max_addr)) { 147 unsigned long max = max_addr - src_addr; 148 long retval; 149 150 user_access_begin(); 151 retval = do_strnlen_user(str, ~0ul, max); 152 user_access_end(); 153 return retval; 154 } 155 return 0; 156 } 157 EXPORT_SYMBOL(strlen_user); 158