lib/strncpy_from_user.c

Source file repositories/reference/linux-study-clean/lib/strncpy_from_user.c

File Facts

System
Linux kernel
Corpus path
lib/strncpy_from_user.c
Extension
.c
Size
4231 bytes
Lines
157
Domain
Kernel Services
Bucket
lib
Inferred role
Kernel Services: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Shared kernel service surface used by multiple subsystems, including helpers, cryptography, virtualization support, and async I/O infrastructure.

Dependency Surface

Detected Declarations

Annotated Snippet

if (has_zero(c, &data, &constants)) {
			data = prep_zero_mask(c, data, &constants);
			data = create_zero_mask(data);
			mask = zero_bytemask(data);
			*(unsigned long *)(dst+res) = c & mask;
			return res + find_zero(data);
		}

		*(unsigned long *)(dst+res) = c;

		res += sizeof(unsigned long);
		max -= sizeof(unsigned long);
	}

byte_at_a_time:
	while (max) {
		char c;

		unsafe_get_user(c,src+res, efault);
		dst[res] = c;
		if (!c)
			return res;
		res++;
		max--;
	}

	/*
	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
	 * too? If so, that's ok - we got as much as the user asked for.
	 */
	if (res >= count)
		return res;

	/*
	 * Nope: we hit the address space limit, and we still had more
	 * characters the caller would have wanted. That's an EFAULT.
	 */
efault:
	return -EFAULT;
}

/**
 * strncpy_from_user: - Copy a NUL terminated string from userspace.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @src:   Source address, in user space.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from userspace to kernel space.
 *
 * On success, returns the length of the string (not including the trailing
 * NUL).
 *
 * If access to userspace fails, returns -EFAULT (some data may have been
 * copied).
 *
 * If @count is smaller than the length of the string, copies @count bytes
 * and returns @count.
 */
long strncpy_from_user(char *dst, const char __user *src, long count)
{
	unsigned long max_addr, src_addr;

	might_fault();
	if (should_fail_usercopy())
		return -EFAULT;
	if (unlikely(count <= 0))
		return 0;

	kasan_check_write(dst, count);
	check_object_size(dst, count, false);

	if (can_do_masked_user_access()) {
		long retval;

		src = masked_user_read_access_begin(src);
		retval = do_strncpy_from_user(dst, src, count, count);
		user_read_access_end();
		return retval;
	}

	max_addr = TASK_SIZE_MAX;
	src_addr = (unsigned long)untagged_addr(src);
	if (likely(src_addr < max_addr)) {
		unsigned long max = max_addr - src_addr;
		long retval;

		/*
		 * Truncate 'max' to the user-specified limit, so that
		 * we only have one limit we need to check in the loop

Annotation

Implementation Notes