| 1 | // SPDX-License-Identifier: GPL-2.0 |
| 2 | #include <linux/compiler.h> |
| 3 | #include <linux/export.h> |
| 4 | #include <linux/fault-inject-usercopy.h> |
| 5 | #include <linux/kasan-checks.h> |
| 6 | #include <linux/thread_info.h> |
| 7 | #include <linux/uaccess.h> |
| 8 | #include <linux/kernel.h> |
| 9 | #include <linux/errno.h> |
| 10 | #include <linux/mm.h> |
| 11 | |
| 12 | #include <asm/byteorder.h> |
| 13 | #include <asm/word-at-a-time.h> |
| 14 | |
| 15 | #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS |
| 16 | #define IS_UNALIGNED(src, dst) 0 |
| 17 | #else |
| 18 | #define IS_UNALIGNED(src, dst) \ |
| 19 | (((long) dst | (long) src) & (sizeof(long) - 1)) |
| 20 | #endif |
| 21 | |
| 22 | /* |
| 23 | * Do a strncpy, return length of string without final '\0'. |
| 24 | * 'count' is the user-supplied count (return 'count' if we |
| 25 | * hit it), 'max' is the address space maximum (and we return |
| 26 | * -EFAULT if we hit it). |
| 27 | */ |
| 28 | static inline long do_strncpy_from_user(char *dst, const char __user *src, |
| 29 | unsigned long count, unsigned long max) |
| 30 | { |
| 31 | const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; |
| 32 | unsigned long res = 0; |
| 33 | |
| 34 | if (IS_UNALIGNED(src, dst)) |
| 35 | goto byte_at_a_time; |
| 36 | |
| 37 | while (max >= sizeof(unsigned long)) { |
| 38 | unsigned long c, data, mask; |
| 39 | |
| 40 | /* Fall back to byte-at-a-time if we get a page fault */ |
| 41 | unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); |
| 42 | |
| 43 | /* |
| 44 | * Note that we mask out the bytes following the NUL. This is |
| 45 | * important to do because string oblivious code may read past |
| 46 | * the NUL. For those routines, we don't want to give them |
| 47 | * potentially random bytes after the NUL in `src`. |
| 48 | * |
| 49 | * One example of such code is BPF map keys. BPF treats map keys |
| 50 | * as an opaque set of bytes. Without the post-NUL mask, any BPF |
| 51 | * maps keyed by strings returned from strncpy_from_user() may |
| 52 | * have multiple entries for semantically identical strings. |
| 53 | */ |
| 54 | if (has_zero(c, &data, &constants)) { |
| 55 | data = prep_zero_mask(c, data, &constants); |
| 56 | data = create_zero_mask(data); |
| 57 | mask = zero_bytemask(data); |
| 58 | *(unsigned long *)(dst+res) = c & mask; |
| 59 | return res + find_zero(data); |
| 60 | } |
| 61 | |
| 62 | *(unsigned long *)(dst+res) = c; |
| 63 | |
| 64 | res += sizeof(unsigned long); |
| 65 | max -= sizeof(unsigned long); |
| 66 | } |
| 67 | |
| 68 | byte_at_a_time: |
| 69 | while (max) { |
| 70 | char c; |
| 71 | |
| 72 | unsafe_get_user(c,src+res, efault); |
| 73 | dst[res] = c; |
| 74 | if (!c) |
| 75 | return res; |
| 76 | res++; |
| 77 | max--; |
| 78 | } |
| 79 | |
| 80 | /* |
| 81 | * Uhhuh. We hit 'max'. But was that the user-specified maximum |
| 82 | * too? If so, that's ok - we got as much as the user asked for. |
| 83 | */ |
| 84 | if (res >= count) |
| 85 | return res; |
| 86 | |
| 87 | /* |
| 88 | * Nope: we hit the address space limit, and we still had more |
| 89 | * characters the caller would have wanted. That's an EFAULT. |
| 90 | */ |
| 91 | efault: |
| 92 | return -EFAULT; |
| 93 | } |
| 94 | |
| 95 | /** |
| 96 | * strncpy_from_user: - Copy a NUL terminated string from userspace. |
| 97 | * @dst: Destination address, in kernel space. This buffer must be at |
| 98 | * least @count bytes long. |
| 99 | * @src: Source address, in user space. |
| 100 | * @count: Maximum number of bytes to copy, including the trailing NUL. |
| 101 | * |
| 102 | * Copies a NUL-terminated string from userspace to kernel space. |
| 103 | * |
| 104 | * On success, returns the length of the string (not including the trailing |
| 105 | * NUL). |
| 106 | * |
| 107 | * If access to userspace fails, returns -EFAULT (some data may have been |
| 108 | * copied). |
| 109 | * |
| 110 | * If @count is smaller than the length of the string, copies @count bytes |
| 111 | * and returns @count. |
| 112 | */ |
| 113 | long strncpy_from_user(char *dst, const char __user *src, long count) |
| 114 | { |
| 115 | unsigned long max_addr, src_addr; |
| 116 | |
| 117 | might_fault(); |
| 118 | if (should_fail_usercopy()) |
| 119 | return -EFAULT; |
| 120 | if (unlikely(count <= 0)) |
| 121 | return 0; |
| 122 | |
| 123 | max_addr = user_addr_max(); |
| 124 | src_addr = (unsigned long)untagged_addr(src); |
| 125 | if (likely(src_addr < max_addr)) { |
| 126 | unsigned long max = max_addr - src_addr; |
| 127 | long retval; |
| 128 | |
| 129 | /* |
| 130 | * Truncate 'max' to the user-specified limit, so that |
| 131 | * we only have one limit we need to check in the loop |
| 132 | */ |
| 133 | if (max > count) |
| 134 | max = count; |
| 135 | |
| 136 | kasan_check_write(dst, count); |
| 137 | check_object_size(dst, count, false); |
| 138 | if (user_read_access_begin(src, max)) { |
| 139 | retval = do_strncpy_from_user(dst, src, count, max); |
| 140 | user_read_access_end(); |
| 141 | return retval; |
| 142 | } |
| 143 | } |
| 144 | return -EFAULT; |
| 145 | } |
| 146 | EXPORT_SYMBOL(strncpy_from_user); |