linux/lib/strnlen_user.c
Peter Zijlstra 226d44acf6 lib/strn*,objtool: Enforce user_access_begin() rules
Apparently GCC can fail to inline a 'static inline' single caller
function:

  lib/strnlen_user.o: warning: objtool: strnlen_user()+0x33: call to do_strnlen_user() with UACCESS enabled
  lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x33: call to do_strncpy_from_user() with UACCESS enabled

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220408094718.262932488@infradead.org
2022-04-19 21:58:47 +02:00

121 lines
3.4 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/uaccess.h>
#include <linux/mm.h>
#include <linux/bitops.h>
#include <asm/word-at-a-time.h>
/*
* Do a strnlen, return length of string *with* final '\0'.
* 'count' is the user-supplied count, while 'max' is the
* address space maximum.
*
* Return 0 for exceptions (which includes hitting the address
* space maximum), or 'count+1' if hitting the user-supplied
* maximum count.
*
* NOTE! We can sometimes overshoot the user-supplied maximum
* if it fits in a aligned 'long'. The caller needs to check
* the return value against "> max".
*/
static __always_inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
{
const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
unsigned long align, res = 0;
unsigned long c;
/*
* Do everything aligned. But that means that we
* need to also expand the maximum..
*/
align = (sizeof(unsigned long) - 1) & (unsigned long)src;
src -= align;
max += align;
unsafe_get_user(c, (unsigned long __user *)src, efault);
c |= aligned_byte_mask(align);
for (;;) {
unsigned long data;
if (has_zero(c, &data, &constants)) {
data = prep_zero_mask(c, data, &constants);
data = create_zero_mask(data);
return res + find_zero(data) + 1 - align;
}
res += sizeof(unsigned long);
/* We already handled 'unsigned long' bytes. Did we do it all ? */
if (unlikely(max <= sizeof(unsigned long)))
break;
max -= sizeof(unsigned long);
unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
}
res -= align;
/*
* Uhhuh. We hit 'max'. But was that the user-specified maximum
* too? If so, return the marker for "too long".
*/
if (res >= count)
return count+1;
/*
* Nope: we hit the address space limit, and we still had more
* characters the caller would have wanted. That's 0.
*/
efault:
return 0;
}
/**
* strnlen_user: - Get the size of a user string INCLUDING final NUL.
* @str: The string to measure.
* @count: Maximum count (including NUL character)
*
* Context: User context only. This function may sleep if pagefaults are
* enabled.
*
* Get the size of a NUL-terminated string in user space.
*
* Returns the size of the string INCLUDING the terminating NUL.
* If the string is too long, returns a number larger than @count. User
* has to check the return value against "> count".
* On exception (or invalid count), returns 0.
*
* NOTE! You should basically never use this function. There is
* almost never any valid case for using the length of a user space
* string, since the string can be changed at any time by other
* threads. Use "strncpy_from_user()" instead to get a stable copy
* of the string.
*/
long strnlen_user(const char __user *str, long count)
{
unsigned long max_addr, src_addr;
if (unlikely(count <= 0))
return 0;
max_addr = TASK_SIZE_MAX;
src_addr = (unsigned long)untagged_addr(str);
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(str, max)) {
retval = do_strnlen_user(str, count, max);
user_read_access_end();
return retval;
}
}
return 0;
}
EXPORT_SYMBOL(strnlen_user);