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Subject[PATCH 2/2] dax: fix bdev NULL pointer dereferences
Date
There are a number of places in dax.c that look up the struct block_device
associated with an inode. Previously this was done by just using
inode->i_sb->s_bdev. This is correct for inodes that exist within the
filesystems supported by DAX (ext2, ext4 & XFS), but when running DAX
against raw block devices this value is NULL. This causes NULL pointer
dereferences when these block_device pointers are used.

Instead, for raw block devices we need to look up the struct block_device
using I_BDEV(). This patch fixes all the block_device lookups in dax.c so
that they work properly for both filesystems and raw block devices.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
fs/dax.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 4fd6b0c..e60a5a7 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -32,6 +32,9 @@
#include <linux/pfn_t.h>
#include <linux/sizes.h>

+#define DAX_BDEV(inode) (S_ISBLK(inode->i_mode) ? I_BDEV(inode) \
+ : inode->i_sb->s_bdev)
+
static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
{
struct request_queue *q = bdev->bd_queue;
@@ -65,7 +68,7 @@ static void dax_unmap_atomic(struct block_device *bdev,
*/
int dax_clear_blocks(struct inode *inode, sector_t block, long _size)
{
- struct block_device *bdev = inode->i_sb->s_bdev;
+ struct block_device *bdev = DAX_BDEV(inode);
struct blk_dax_ctl dax = {
.sector = block << (inode->i_blkbits - 9),
.size = _size,
@@ -246,7 +249,7 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
loff_t end = pos + iov_iter_count(iter);

memset(&bh, 0, sizeof(bh));
- bh.b_bdev = inode->i_sb->s_bdev;
+ bh.b_bdev = DAX_BDEV(inode);

if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
struct address_space *mapping = inode->i_mapping;
@@ -468,7 +471,7 @@ int dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
loff_t end)
{
struct inode *inode = mapping->host;
- struct block_device *bdev = inode->i_sb->s_bdev;
+ struct block_device *bdev = DAX_BDEV(inode);
pgoff_t start_index, end_index, pmd_index;
pgoff_t indices[PAGEVEC_SIZE];
struct pagevec pvec;
@@ -608,7 +611,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,

memset(&bh, 0, sizeof(bh));
block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
- bh.b_bdev = inode->i_sb->s_bdev;
+ bh.b_bdev = DAX_BDEV(inode);
bh.b_size = PAGE_SIZE;

repeat:
@@ -827,7 +830,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
}

memset(&bh, 0, sizeof(bh));
- bh.b_bdev = inode->i_sb->s_bdev;
+ bh.b_bdev = DAX_BDEV(inode);
block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);

bh.b_size = PMD_SIZE;
@@ -1080,7 +1083,7 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
BUG_ON((offset + length) > PAGE_CACHE_SIZE);

memset(&bh, 0, sizeof(bh));
- bh.b_bdev = inode->i_sb->s_bdev;
+ bh.b_bdev = DAX_BDEV(inode);
bh.b_size = PAGE_CACHE_SIZE;
err = get_block(inode, index, &bh, 0);
if (err < 0)
--
2.5.0
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