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146 lines
3.9 KiB
146 lines
3.9 KiB
// SPDX-License-Identifier: GPL-2.0 |
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#include <linux/compiler.h> |
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#include <linux/export.h> |
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#include <linux/fault-inject-usercopy.h> |
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#include <linux/kasan-checks.h> |
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#include <linux/thread_info.h> |
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#include <linux/uaccess.h> |
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#include <linux/kernel.h> |
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#include <linux/errno.h> |
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#include <linux/mm.h> |
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#include <asm/byteorder.h> |
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#include <asm/word-at-a-time.h> |
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#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS |
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#define IS_UNALIGNED(src, dst) 0 |
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#else |
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#define IS_UNALIGNED(src, dst) \ |
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(((long) dst | (long) src) & (sizeof(long) - 1)) |
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#endif |
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/* |
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* Do a strncpy, return length of string without final '\0'. |
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* 'count' is the user-supplied count (return 'count' if we |
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* hit it), 'max' is the address space maximum (and we return |
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* -EFAULT if we hit it). |
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*/ |
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static __always_inline long do_strncpy_from_user(char *dst, const char __user *src, |
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unsigned long count, unsigned long max) |
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{ |
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const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; |
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unsigned long res = 0; |
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if (IS_UNALIGNED(src, dst)) |
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goto byte_at_a_time; |
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while (max >= sizeof(unsigned long)) { |
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unsigned long c, data, mask; |
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/* Fall back to byte-at-a-time if we get a page fault */ |
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unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); |
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/* |
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* Note that we mask out the bytes following the NUL. This is |
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* important to do because string oblivious code may read past |
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* the NUL. For those routines, we don't want to give them |
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* potentially random bytes after the NUL in `src`. |
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* |
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* One example of such code is BPF map keys. BPF treats map keys |
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* as an opaque set of bytes. Without the post-NUL mask, any BPF |
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* maps keyed by strings returned from strncpy_from_user() may |
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* have multiple entries for semantically identical strings. |
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*/ |
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if (has_zero(c, &data, &constants)) { |
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data = prep_zero_mask(c, data, &constants); |
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data = create_zero_mask(data); |
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mask = zero_bytemask(data); |
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*(unsigned long *)(dst+res) = c & mask; |
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return res + find_zero(data); |
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} |
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*(unsigned long *)(dst+res) = c; |
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res += sizeof(unsigned long); |
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max -= sizeof(unsigned long); |
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} |
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byte_at_a_time: |
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while (max) { |
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char c; |
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unsafe_get_user(c,src+res, efault); |
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dst[res] = c; |
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if (!c) |
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return res; |
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res++; |
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max--; |
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} |
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/* |
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* Uhhuh. We hit 'max'. But was that the user-specified maximum |
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* too? If so, that's ok - we got as much as the user asked for. |
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*/ |
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if (res >= count) |
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return res; |
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/* |
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* Nope: we hit the address space limit, and we still had more |
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* characters the caller would have wanted. That's an EFAULT. |
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*/ |
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efault: |
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return -EFAULT; |
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} |
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/** |
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* strncpy_from_user: - Copy a NUL terminated string from userspace. |
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* @dst: Destination address, in kernel space. This buffer must be at |
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* least @count bytes long. |
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* @src: Source address, in user space. |
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* @count: Maximum number of bytes to copy, including the trailing NUL. |
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* |
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* Copies a NUL-terminated string from userspace to kernel space. |
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* |
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* On success, returns the length of the string (not including the trailing |
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* NUL). |
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* |
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* If access to userspace fails, returns -EFAULT (some data may have been |
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* copied). |
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* |
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* If @count is smaller than the length of the string, copies @count bytes |
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* and returns @count. |
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*/ |
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long strncpy_from_user(char *dst, const char __user *src, long count) |
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{ |
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unsigned long max_addr, src_addr; |
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might_fault(); |
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if (should_fail_usercopy()) |
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return -EFAULT; |
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if (unlikely(count <= 0)) |
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return 0; |
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max_addr = TASK_SIZE_MAX; |
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src_addr = (unsigned long)untagged_addr(src); |
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if (likely(src_addr < max_addr)) { |
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unsigned long max = max_addr - src_addr; |
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long retval; |
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/* |
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* Truncate 'max' to the user-specified limit, so that |
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* we only have one limit we need to check in the loop |
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*/ |
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if (max > count) |
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max = count; |
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kasan_check_write(dst, count); |
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check_object_size(dst, count, false); |
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if (user_read_access_begin(src, max)) { |
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retval = do_strncpy_from_user(dst, src, count, max); |
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user_read_access_end(); |
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return retval; |
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} |
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} |
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return -EFAULT; |
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} |
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EXPORT_SYMBOL(strncpy_from_user);
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