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, long count, unsigned long max) 27 { 28 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; 29 long res = 0; 30 31 /* 32 * Truncate 'max' to the user-specified limit, so that 33 * we only have one limit we need to check in the loop 34 */ 35 if (max > count) 36 max = count; 37 38 if (IS_UNALIGNED(src, dst)) 39 goto byte_at_a_time; 40 41 while (max >= sizeof(unsigned long)) { 42 unsigned long c, data; 43 44 /* Fall back to byte-at-a-time if we get a page fault */ 45 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); 46 47 *(unsigned long *)(dst+res) = c; 48 if (has_zero(c, &data, &constants)) { 49 data = prep_zero_mask(c, data, &constants); 50 data = create_zero_mask(data); 51 return res + find_zero(data); 52 } 53 res += sizeof(unsigned long); 54 max -= sizeof(unsigned long); 55 } 56 57 byte_at_a_time: 58 while (max) { 59 char c; 60 61 unsafe_get_user(c,src+res, efault); 62 dst[res] = c; 63 if (!c) 64 return res; 65 res++; 66 max--; 67 } 68 69 /* 70 * Uhhuh. We hit 'max'. But was that the user-specified maximum 71 * too? If so, that's ok - we got as much as the user asked for. 72 */ 73 if (res >= count) 74 return res; 75 76 /* 77 * Nope: we hit the address space limit, and we still had more 78 * characters the caller would have wanted. That's an EFAULT. 79 */ 80 efault: 81 return -EFAULT; 82 } 83 84 /** 85 * strncpy_from_user: - Copy a NUL terminated string from userspace. 86 * @dst: Destination address, in kernel space. This buffer must be at 87 * least @count bytes long. 88 * @src: Source address, in user space. 89 * @count: Maximum number of bytes to copy, including the trailing NUL. 90 * 91 * Copies a NUL-terminated string from userspace to kernel space. 92 * 93 * On success, returns the length of the string (not including the trailing 94 * NUL). 95 * 96 * If access to userspace fails, returns -EFAULT (some data may have been 97 * copied). 98 * 99 * If @count is smaller than the length of the string, copies @count bytes 100 * and returns @count. 101 */ 102 long strncpy_from_user(char *dst, const char __user *src, long count) 103 { 104 unsigned long max_addr, src_addr; 105 106 if (unlikely(count <= 0)) 107 return 0; 108 109 max_addr = user_addr_max(); 110 src_addr = (unsigned long)src; 111 if (likely(src_addr < max_addr)) { 112 unsigned long max = max_addr - src_addr; 113 long retval; 114 115 kasan_check_write(dst, count); 116 check_object_size(dst, count, false); 117 if (user_access_begin(src, max)) { 118 retval = do_strncpy_from_user(dst, src, count, max); 119 user_access_end(); 120 return retval; 121 } 122 } 123 return -EFAULT; 124 } 125 EXPORT_SYMBOL(strncpy_from_user); 126