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fix fault_in_multipages_...() on architectures with no-op access_ok()

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Switching iov_iter fault-in to multipages variants has exposed an old
bug in underlying fault_in_multipages_...(); they break if the range
passed to them wraps around.  Normally access_ok() done by callers will
prevent such (and it's a guaranteed EFAULT - ERR_PTR() values fall into
such a range and they should not point to any valid objects).

However, on architectures where userland and kernel live in different
MMU contexts (e.g. s390) access_ok() is a no-op and on those a range
with a wraparound can reach fault_in_multipages_...().

Since any wraparound means EFAULT there, the fix is trivial - turn
those

    while (uaddr <= end)
	    ...
into

    if (unlikely(uaddr > end))
	    return -EFAULT;
    do
	    ...
    while (uaddr <= end);

Reported-by: Jan Stancek <jstancek@redhat.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Al Viro 2016-09-20 20:07:42 +01:00 committed by Linus Torvalds
parent df04abfd18
commit e23d4159b1
1 changed files with 19 additions and 19 deletions
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38
include/linux/pagemap.h
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@ -571,56 +571,56 @@ static inline int fault_in_pages_readable(const char __user *uaddr, int size)
*/
static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
{
int ret = 0;
char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return ret;
return 0;
if (unlikely(uaddr > end))
return -EFAULT;
/*
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
while (uaddr <= end) {
ret = __put_user(0, uaddr);
if (ret != 0)
return ret;
do {
if (unlikely(__put_user(0, uaddr) != 0))
return -EFAULT;
uaddr += PAGE_SIZE;
}
} while (uaddr <= end);
/* Check whether the range spilled into the next page. */
if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK))
ret = __put_user(0, end);
return __put_user(0, end);
return ret;
return 0;
}
static inline int fault_in_multipages_readable(const char __user *uaddr,
int size)
{
volatile char c;
int ret = 0;
const char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return ret;
return 0;
while (uaddr <= end) {
ret = __get_user(c, uaddr);
if (ret != 0)
return ret;
if (unlikely(uaddr > end))
return -EFAULT;
do {
if (unlikely(__get_user(c, uaddr) != 0))
return -EFAULT;
uaddr += PAGE_SIZE;
}
} while (uaddr <= end);
/* Check whether the range spilled into the next page. */
if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK)) {
ret = __get_user(c, end);
(void)c;
return __get_user(c, end);
}
return ret;
return 0;
}
int add_to_page_cache_locked(struct page *page, struct address_space *mapping,