From e23d4159b109167126e5bcd7f3775c95de7fee47 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Tue, 20 Sep 2016 20:07:42 +0100 Subject: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok() 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 Tested-by: Jan Stancek Cc: stable@vger.kernel.org # v3.5+ Signed-off-by: Al Viro Signed-off-by: Linus Torvalds --- include/linux/pagemap.h | 38 +++++++++++++++++++------------------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 66a1260b33de..7e3d53753612 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -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, -- 2.20.1