1 #include <linux/compiler.h> 2 #include <linux/export.h> 3 #include <linux/kasan-checks.h> 4 #include <linux/thread_info.h> 5 #include <linux/uaccess.h> 6 #include <linux/kernel.h> 7 #include <linux/errno.h> 8 9 #include <asm/byteorder.h> 10 #include <asm/word-at-a-time.h> 11 12 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS 13 #define IS_UNALIGNED(src, dst) 0 14 #else 15 #define IS_UNALIGNED(src, dst) \ 16 (((long) dst | (long) src) & (sizeof(long) - 1)) 17 #endif 18 19 /* 20 * Do a strncpy, return length of string without final '\0'. 21 * 'count' is the user-supplied count (return 'count' if we 22 * hit it), 'max' is the address space maximum (and we return 23 * -EFAULT if we hit it). 24 */ 25 static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max) 26 { 27 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; 28 long res = 0; 29 30 /* 31 * Truncate 'max' to the user-specified limit, so that 32 * we only have one limit we need to check in the loop 33 */ 34 if (max > count) 35 max = count; 36 37 if (IS_UNALIGNED(src, dst)) 38 goto byte_at_a_time; 39 40 while (max >= sizeof(unsigned long)) { 41 unsigned long c, data; 42 43 /* Fall back to byte-at-a-time if we get a page fault */ 44 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); 45 46 *(unsigned long *)(dst+res) = c; 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); 51 } 52 res += sizeof(unsigned long); 53 max -= sizeof(unsigned long); 54 } 55 56 byte_at_a_time: 57 while (max) { 58 char c; 59 60 unsafe_get_user(c,src+res, efault); 61 dst[res] = c; 62 if (!c) 63 return res; 64 res++; 65 max--; 66 } 67 68 /* 69 * Uhhuh. We hit 'max'. But was that the user-specified maximum 70 * too? If so, that's ok - we got as much as the user asked for. 71 */ 72 if (res >= count) 73 return res; 74 75 /* 76 * Nope: we hit the address space limit, and we still had more 77 * characters the caller would have wanted. That's an EFAULT. 78 */ 79 efault: 80 return -EFAULT; 81 } 82 83 /** 84 * strncpy_from_user: - Copy a NUL terminated string from userspace. 85 * @dst: Destination address, in kernel space. This buffer must be at 86 * least @count bytes long. 87 * @src: Source address, in user space. 88 * @count: Maximum number of bytes to copy, including the trailing NUL. 89 * 90 * Copies a NUL-terminated string from userspace to kernel space. 91 * 92 * On success, returns the length of the string (not including the trailing 93 * NUL). 94 * 95 * If access to userspace fails, returns -EFAULT (some data may have been 96 * copied). 97 * 98 * If @count is smaller than the length of the string, copies @count bytes 99 * and returns @count. 100 */ 101 long strncpy_from_user(char *dst, const char __user *src, long count) 102 { 103 unsigned long max_addr, src_addr; 104 105 if (unlikely(count <= 0)) 106 return 0; 107 108 max_addr = user_addr_max(); 109 src_addr = (unsigned long)src; 110 if (likely(src_addr < max_addr)) { 111 unsigned long max = max_addr - src_addr; 112 long retval; 113 114 kasan_check_write(dst, count); 115 check_object_size(dst, count, false); 116 user_access_begin(); 117 retval = do_strncpy_from_user(dst, src, count, max); 118 user_access_end(); 119 return retval; 120 } 121 return -EFAULT; 122 } 123 EXPORT_SYMBOL(strncpy_from_user); 124