1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/compiler.h> 3 #include <linux/export.h> 4 #include <linux/kasan-checks.h> 5 #include <linux/thread_info.h> 6 #include <linux/uaccess.h> 7 #include <linux/kernel.h> 8 #include <linux/errno.h> 9 10 #include <asm/byteorder.h> 11 #include <asm/word-at-a-time.h> 12 13 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS 14 #define IS_UNALIGNED(src, dst) 0 15 #else 16 #define IS_UNALIGNED(src, dst) \ 17 (((long) dst | (long) src) & (sizeof(long) - 1)) 18 #endif 19 20 /* 21 * Do a strncpy, return length of string without final '\0'. 22 * 'count' is the user-supplied count (return 'count' if we 23 * hit it), 'max' is the address space maximum (and we return 24 * -EFAULT if we hit it). 25 */ 26 static inline long do_strncpy_from_user(char *dst, const char __user *src, 27 unsigned long count, unsigned long max) 28 { 29 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; 30 unsigned long res = 0; 31 32 /* 33 * Truncate 'max' to the user-specified limit, so that 34 * we only have one limit we need to check in the loop 35 */ 36 if (max > count) 37 max = count; 38 39 if (IS_UNALIGNED(src, dst)) 40 goto byte_at_a_time; 41 42 while (max >= sizeof(unsigned long)) { 43 unsigned long c, data; 44 45 /* Fall back to byte-at-a-time if we get a page fault */ 46 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); 47 48 *(unsigned long *)(dst+res) = c; 49 if (has_zero(c, &data, &constants)) { 50 data = prep_zero_mask(c, data, &constants); 51 data = create_zero_mask(data); 52 return res + find_zero(data); 53 } 54 res += sizeof(unsigned long); 55 max -= sizeof(unsigned long); 56 } 57 58 byte_at_a_time: 59 while (max) { 60 char c; 61 62 unsafe_get_user(c,src+res, efault); 63 dst[res] = c; 64 if (!c) 65 return res; 66 res++; 67 max--; 68 } 69 70 /* 71 * Uhhuh. We hit 'max'. But was that the user-specified maximum 72 * too? If so, that's ok - we got as much as the user asked for. 73 */ 74 if (res >= count) 75 return res; 76 77 /* 78 * Nope: we hit the address space limit, and we still had more 79 * characters the caller would have wanted. That's an EFAULT. 80 */ 81 efault: 82 return -EFAULT; 83 } 84 85 /** 86 * strncpy_from_user: - Copy a NUL terminated string from userspace. 87 * @dst: Destination address, in kernel space. This buffer must be at 88 * least @count bytes long. 89 * @src: Source address, in user space. 90 * @count: Maximum number of bytes to copy, including the trailing NUL. 91 * 92 * Copies a NUL-terminated string from userspace to kernel space. 93 * 94 * On success, returns the length of the string (not including the trailing 95 * NUL). 96 * 97 * If access to userspace fails, returns -EFAULT (some data may have been 98 * copied). 99 * 100 * If @count is smaller than the length of the string, copies @count bytes 101 * and returns @count. 102 */ 103 long strncpy_from_user(char *dst, const char __user *src, 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)src; 112 if (likely(src_addr < max_addr)) { 113 unsigned long max = max_addr - src_addr; 114 long retval; 115 116 kasan_check_write(dst, count); 117 check_object_size(dst, count, false); 118 if (user_access_begin(src, max)) { 119 retval = do_strncpy_from_user(dst, src, count, max); 120 user_access_end(); 121 return retval; 122 } 123 } 124 return -EFAULT; 125 } 126 EXPORT_SYMBOL(strncpy_from_user); 127