linux/lib/usercopy.c
Christophe Leroy 41cd780524 uaccess: Selectively open read or write user access
When opening user access to only perform reads, only open read access.
When opening user access to only perform writes, only open write
access.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2e73bc57125c2c6ab12a587586a4eed3a47105fc.1585898438.git.christophe.leroy@c-s.fr
2020-05-01 12:35:21 +10:00

89 lines
2.0 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/uaccess.h>
#include <linux/bitops.h>
/* out-of-line parts */
#ifndef INLINE_COPY_FROM_USER
unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
{
unsigned long res = n;
might_fault();
if (likely(access_ok(from, n))) {
kasan_check_write(to, n);
res = raw_copy_from_user(to, from, n);
}
if (unlikely(res))
memset(to + (n - res), 0, res);
return res;
}
EXPORT_SYMBOL(_copy_from_user);
#endif
#ifndef INLINE_COPY_TO_USER
unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
{
might_fault();
if (likely(access_ok(to, n))) {
kasan_check_read(from, n);
n = raw_copy_to_user(to, from, n);
}
return n;
}
EXPORT_SYMBOL(_copy_to_user);
#endif
/**
* check_zeroed_user: check if a userspace buffer only contains zero bytes
* @from: Source address, in userspace.
* @size: Size of buffer.
*
* This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
* userspace addresses (and is more efficient because we don't care where the
* first non-zero byte is).
*
* Returns:
* * 0: There were non-zero bytes present in the buffer.
* * 1: The buffer was full of zero bytes.
* * -EFAULT: access to userspace failed.
*/
int check_zeroed_user(const void __user *from, size_t size)
{
unsigned long val;
uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
if (unlikely(size == 0))
return 1;
from -= align;
size += align;
if (!user_read_access_begin(from, size))
return -EFAULT;
unsafe_get_user(val, (unsigned long __user *) from, err_fault);
if (align)
val &= ~aligned_byte_mask(align);
while (size > sizeof(unsigned long)) {
if (unlikely(val))
goto done;
from += sizeof(unsigned long);
size -= sizeof(unsigned long);
unsafe_get_user(val, (unsigned long __user *) from, err_fault);
}
if (size < sizeof(unsigned long))
val &= aligned_byte_mask(size);
done:
user_read_access_end();
return (val == 0);
err_fault:
user_read_access_end();
return -EFAULT;
}
EXPORT_SYMBOL(check_zeroed_user);