From: Jeff Moyer <jmoyer@redhat.com>
Date: Wed, 15 Nov 2017 01:37:27 +0000 (-0500)
Subject: dax: fix PMD faults on zero-length files
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=c21261e6311a7d237da47b608e933f3abd7e534e;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git

dax: fix PMD faults on zero-length files

commit 957ac8c421ad8b5eef9b17fe98e146d8311a541e upstream.

PMD faults on a zero length file on a file system mounted with -o dax
will not generate SIGBUS as expected.

	fd = open(...O_TRUNC);
	addr = mmap(NULL, 2*1024*1024, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
	*addr = 'a';
        <expect SIGBUS>

The problem is this code in dax_iomap_pmd_fault:

	max_pgoff = (i_size_read(inode) - 1) >> PAGE_SHIFT;

If the inode size is zero, we end up with a max_pgoff that is way larger
than 0.  :)  Fix it by using DIV_ROUND_UP, as is done elsewhere in the
kernel.

I tested this with some simple test code that ensured that SIGBUS was
received where expected.

Fixes: 642261ac995e ("dax: add struct iomap based DAX PMD support")
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/dax.c b/fs/dax.c
index f001d8c72a06..191306cd8b6b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1327,7 +1327,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf,
 	 * this is a reliable test.
 	 */
 	pgoff = linear_page_index(vma, pmd_addr);
-	max_pgoff = (i_size_read(inode) - 1) >> PAGE_SHIFT;
+	max_pgoff = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 
 	trace_dax_pmd_fault(inode, vmf, max_pgoff, 0);
 
@@ -1351,13 +1351,13 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf,
 	if ((pmd_addr + PMD_SIZE) > vma->vm_end)
 		goto fallback;
 
-	if (pgoff > max_pgoff) {
+	if (pgoff >= max_pgoff) {
 		result = VM_FAULT_SIGBUS;
 		goto out;
 	}
 
 	/* If the PMD would extend beyond the file size */
-	if ((pgoff | PG_PMD_COLOUR) > max_pgoff)
+	if ((pgoff | PG_PMD_COLOUR) >= max_pgoff)
 		goto fallback;
 
 	/*