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 #include <linux/mm.h> 10 11 #include <asm/byteorder.h> 12 #include <asm/word-at-a-time.h> 13 14 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS 15 #define IS_UNALIGNED(src, dst) 0 16 #else 17 #define IS_UNALIGNED(src, dst) \ 18 (((long) dst | (long) src) & (sizeof(long) - 1)) 19 #endif 20 21 /* 22 * Do a strncpy, return length of string without final '\0'. 23 * 'count' is the user-supplied count (return 'count' if we 24 * hit it), 'max' is the address space maximum (and we return 25 * -EFAULT if we hit it). 26 */ 27 static inline long do_strncpy_from_user(char *dst, const char __user *src, 28 unsigned long count, unsigned long max) 29 { 30 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; 31 unsigned long res = 0; 32 33 if (IS_UNALIGNED(src, dst)) 34 goto byte_at_a_time; 35 36 while (max >= sizeof(unsigned long)) { 37 unsigned long c, data; 38 39 /* Fall back to byte-at-a-time if we get a page fault */ 40 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); 41 42 *(unsigned long *)(dst+res) = c; 43 if (has_zero(c, &data, &constants)) { 44 data = prep_zero_mask(c, data, &constants); 45 data = create_zero_mask(data); 46 return res + find_zero(data); 47 } 48 res += sizeof(unsigned long); 49 max -= sizeof(unsigned long); 50 } 51 52 byte_at_a_time: 53 while (max) { 54 char c; 55 56 unsafe_get_user(c,src+res, efault); 57 dst[res] = c; 58 if (!c) 59 return res; 60 res++; 61 max--; 62 } 63 64 /* 65 * Uhhuh. We hit 'max'. But was that the user-specified maximum 66 * too? If so, that's ok - we got as much as the user asked for. 67 */ 68 if (res >= count) 69 return res; 70 71 /* 72 * Nope: we hit the address space limit, and we still had more 73 * characters the caller would have wanted. That's an EFAULT. 74 */ 75 efault: 76 return -EFAULT; 77 } 78 79 /** 80 * strncpy_from_user: - Copy a NUL terminated string from userspace. 81 * @dst: Destination address, in kernel space. This buffer must be at 82 * least @count bytes long. 83 * @src: Source address, in user space. 84 * @count: Maximum number of bytes to copy, including the trailing NUL. 85 * 86 * Copies a NUL-terminated string from userspace to kernel space. 87 * 88 * On success, returns the length of the string (not including the trailing 89 * NUL). 90 * 91 * If access to userspace fails, returns -EFAULT (some data may have been 92 * copied). 93 * 94 * If @count is smaller than the length of the string, copies @count bytes 95 * and returns @count. 96 */ 97 long strncpy_from_user(char *dst, const char __user *src, 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)untagged_addr(src); 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 kasan_check_write(dst, count); 118 check_object_size(dst, count, false); 119 if (user_access_begin(src, max)) { 120 retval = do_strncpy_from_user(dst, src, count, max); 121 user_access_end(); 122 return retval; 123 } 124 } 125 return -EFAULT; 126 } 127 EXPORT_SYMBOL(strncpy_from_user); 128