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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157// 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);