// SPDX-License-Identifier: GPL-2.0#include <linux/compiler.h>#include <linux/export.h>#include <linux/fault-inject-usercopy.h>#include <linux/kasan-checks.h>#include <linux/thread_info.h>#include <linux/uaccess.h>#include <linux/kernel.h>#include <linux/errno.h>#include <linux/mm.h> #include <asm/byteorder.h>#include <asm/word-at-a-time.h> #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS#define IS_UNALIGNED(src, dst)	0#else#define IS_UNALIGNED(src, dst)	\	(((long) dst | (long) src) & (sizeof(long) - 1))#endif /* * Do a strncpy, return length of string without final '\0'. * 'count' is the user-supplied count (return 'count' if we * hit it), 'max' is the address space maximum (and we return * -EFAULT if we hit it). */static __always_inline long do_strncpy_from_user(char *dst, const char __user *src,					unsigned long count, unsigned long max){	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;	unsigned long res = 0; 	if (IS_UNALIGNED(src, dst))		goto byte_at_a_time; 	while (max >= sizeof(unsigned long)) {		unsigned long c, data, mask; 		/* Fall back to byte-at-a-time if we get a page fault */		unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); 		/*		 * Note that we mask out the bytes following the NUL. This is		 * important to do because string oblivious code may read past		 * the NUL. For those routines, we don't want to give them		 * potentially random bytes after the NUL in `src`.		 *		 * One example of such code is BPF map keys. BPF treats map keys		 * as an opaque set of bytes. Without the post-NUL mask, any BPF		 * maps keyed by strings returned from strncpy_from_user() may		 * have multiple entries for semantically identical strings.		 */		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		 */		if (max > count)			max = count; 		if (user_read_access_begin(src, max)) {			retval = do_strncpy_from_user(dst, src, count, max);			user_read_access_end();			return retval;		}	}	return -EFAULT;}EXPORT_SYMBOL(strncpy_from_user);