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git.proxmox.com Git - mirror_ubuntu-eoan-kernel.git/blob - lib/strnlen_user.c
1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/kernel.h>
3 #include <linux/export.h>
4 #include <linux/uaccess.h>
6 #include <asm/word-at-a-time.h>
8 /* Set bits in the first 'n' bytes when loaded from memory */
10 # define aligned_byte_mask(n) ((1ul << 8*(n))-1)
12 # define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
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.
20 * Return 0 for exceptions (which includes hitting the address
21 * space maximum), or 'count+1' if hitting the user-supplied
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".
28 static inline long do_strnlen_user(const char __user
*src
, unsigned long count
, unsigned long max
)
30 const struct word_at_a_time constants
= WORD_AT_A_TIME_CONSTANTS
;
35 * Truncate 'max' to the user-specified limit, so that
36 * we only have one limit we need to check in the loop
42 * Do everything aligned. But that means that we
43 * need to also expand the maximum..
45 align
= (sizeof(long) - 1) & (unsigned long)src
;
49 unsafe_get_user(c
, (unsigned long __user
*)src
, efault
);
50 c
|= aligned_byte_mask(align
);
54 if (has_zero(c
, &data
, &constants
)) {
55 data
= prep_zero_mask(c
, data
, &constants
);
56 data
= create_zero_mask(data
);
57 return res
+ find_zero(data
) + 1 - align
;
59 res
+= sizeof(unsigned long);
60 /* We already handled 'unsigned long' bytes. Did we do it all ? */
61 if (unlikely(max
<= sizeof(unsigned long)))
63 max
-= sizeof(unsigned long);
64 unsafe_get_user(c
, (unsigned long __user
*)(src
+res
), efault
);
69 * Uhhuh. We hit 'max'. But was that the user-specified maximum
70 * too? If so, return the marker for "too long".
76 * Nope: we hit the address space limit, and we still had more
77 * characters the caller would have wanted. That's 0.
84 * strnlen_user: - Get the size of a user string INCLUDING final NUL.
85 * @str: The string to measure.
86 * @count: Maximum count (including NUL character)
88 * Context: User context only. This function may sleep if pagefaults are
91 * Get the size of a NUL-terminated string in user space.
93 * Returns the size of the string INCLUDING the terminating NUL.
94 * If the string is too long, returns a number larger than @count. User
95 * has to check the return value against "> count".
96 * On exception (or invalid count), returns 0.
98 * NOTE! You should basically never use this function. There is
99 * almost never any valid case for using the length of a user space
100 * string, since the string can be changed at any time by other
101 * threads. Use "strncpy_from_user()" instead to get a stable copy
104 long strnlen_user(const char __user
*str
, long count
)
106 unsigned long max_addr
, src_addr
;
108 if (unlikely(count
<= 0))
111 max_addr
= user_addr_max();
112 src_addr
= (unsigned long)str
;
113 if (likely(src_addr
< max_addr
)) {
114 unsigned long max
= max_addr
- src_addr
;
117 if (user_access_begin(str
, max
)) {
118 retval
= do_strnlen_user(str
, count
, max
);
125 EXPORT_SYMBOL(strnlen_user
);