linux-kernel - [PATCH v2] hugetlbfs: fix bug in pgoff overflow checking

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Date:   Fri, 30 Mar 2018 07:54:02 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Michal Hocko <mhocko@...nel.org>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nic Losby <blurbdust@...il.com>, Dan Rue <dan.rue@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>, stable@...r.kernel.org
Subject: [PATCH v2] hugetlbfs: fix bug in pgoff overflow checking

This is a fix for a regression in 32 bit kernels caused by an
invalid check for pgoff overflow in hugetlbfs mmap setup.  The
check incorrectly specified that the size of a loff_t was the
same as the size of a long.  The regression prevents mapping
hugetlbfs files at offsets greater than 4GB on 32 bit kernels.

On 32 bit kernels conversion from a page based unsigned long can
not overflow a loff_t byte offset.  Therefore, skip this check
if sizeof(unsigned long) != sizeof(loff_t).

Fixes: 63489f8e8211 ("hugetlbfs: check for pgoff value overflow")
Cc: <stable@...r.kernel.org>
Reported-by: Dan Rue <dan.rue@...aro.org>
Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 fs/hugetlbfs/inode.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index b9a254dcc0e7..d508c7844681 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -138,10 +138,14 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
 
 	/*
 	 * page based offset in vm_pgoff could be sufficiently large to
-	 * overflow a (l)off_t when converted to byte offset.
+	 * overflow a loff_t when converted to byte offset.  This can
+	 * only happen on architectures where sizeof(loff_t) ==
+	 * sizeof(unsigned long).  So, only check in those instances.
 	 */
-	if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
-		return -EINVAL;
+	if (sizeof(unsigned long) == sizeof(loff_t)) {
+		if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
+			return -EINVAL;
+	}
 
 	/* must be huge page aligned */
 	if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
-- 
2.13.6