1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/kernel.h>
3 #include <linux/export.h>
4 #include <linux/uaccess.h>
5
6 #include <asm/word-at-a-time.h>
7
8 /* Set bits in the first 'n' bytes when loaded from memory */
9 #ifdef __LITTLE_ENDIAN
10 # define aligned_byte_mask(n) ((1ul << 8*(n))-1)
11 #else
12 # define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
13 #endif
14
15 /*
16 * Do a strnlen, return length of string *with* final '\0'.
17 * 'count' is the user-supplied count, while 'max' is the
18 * address space maximum.
19 *
20 * Return 0 for exceptions (which includes hitting the address
21 * space maximum), or 'count+1' if hitting the user-supplied
22 * maximum count.
23 *
24 * NOTE! We can sometimes overshoot the user-supplied maximum
25 * if it fits in a aligned 'long'. The caller needs to check
26 * the return value against "> max".
27 */
do_strnlen_user(const char __user * src,unsigned long count,unsigned long max)28 static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
29 {
30 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
31 unsigned long align, res = 0;
32 unsigned long c;
33
34 /*
35 * Do everything aligned. But that means that we
36 * need to also expand the maximum..
37 */
38 align = (sizeof(unsigned long) - 1) & (unsigned long)src;
39 src -= align;
40 max += align;
41
42 unsafe_get_user(c, (unsigned long __user *)src, efault);
43 c |= aligned_byte_mask(align);
44
45 for (;;) {
46 unsigned long data;
47 if (has_zero(c, &data, &constants)) {
48 data = prep_zero_mask(c, data, &constants);
49 data = create_zero_mask(data);
50 return res + find_zero(data) + 1 - align;
51 }
52 res += sizeof(unsigned long);
53 /* We already handled 'unsigned long' bytes. Did we do it all ? */
54 if (unlikely(max <= sizeof(unsigned long)))
55 break;
56 max -= sizeof(unsigned long);
57 unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
58 }
59 res -= align;
60
61 /*
62 * Uhhuh. We hit 'max'. But was that the user-specified maximum
63 * too? If so, return the marker for "too long".
64 */
65 if (res >= count)
66 return count+1;
67
68 /*
69 * Nope: we hit the address space limit, and we still had more
70 * characters the caller would have wanted. That's 0.
71 */
72 efault:
73 return 0;
74 }
75
76 /**
77 * strnlen_user: - Get the size of a user string INCLUDING final NUL.
78 * @str: The string to measure.
79 * @count: Maximum count (including NUL character)
80 *
81 * Context: User context only. This function may sleep if pagefaults are
82 * enabled.
83 *
84 * Get the size of a NUL-terminated string in user space.
85 *
86 * Returns the size of the string INCLUDING the terminating NUL.
87 * If the string is too long, returns a number larger than @count. User
88 * has to check the return value against "> count".
89 * On exception (or invalid count), returns 0.
90 *
91 * NOTE! You should basically never use this function. There is
92 * almost never any valid case for using the length of a user space
93 * string, since the string can be changed at any time by other
94 * threads. Use "strncpy_from_user()" instead to get a stable copy
95 * of the string.
96 */
strnlen_user(const char __user * str,long count)97 long strnlen_user(const char __user *str, long count)
98 {
99 unsigned long max_addr, src_addr;
100
101 if (unlikely(count <= 0))
102 return 0;
103
104 max_addr = user_addr_max();
105 src_addr = (unsigned long)str;
106 if (likely(src_addr < max_addr)) {
107 unsigned long max = max_addr - src_addr;
108 long retval;
109
110 /*
111 * Truncate 'max' to the user-specified limit, so that
112 * we only have one limit we need to check in the loop
113 */
114 if (max > count)
115 max = count;
116
117 if (user_access_begin(VERIFY_READ, str, max)) {
118 retval = do_strnlen_user(str, count, max);
119 user_access_end();
120 return retval;
121 }
122 }
123 return 0;
124 }
125 EXPORT_SYMBOL(strnlen_user);
126