The patch titled
Subject: dax: fix NULL pointer dereference in __dax_dbg()
has been added to the -mm tree. Its filename is
dax-fix-null-pointer-dereference-in-__dax_dbg.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dax-fix-null-pointer-dereference-in-__dax_dbg.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dax-fix-null-pointer-dereference-in-__dax_dbg.patch
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From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: dax: fix NULL pointer dereference in __dax_dbg()
In __dax_pmd_fault() we currently assume that get_block() will always set
bh.b_bdev and we unconditionally dereference it in __dax_dbg(). This
assumption isn't always true - when called for reads of holes
ext4_dax_mmap_get_block() returns a buffer head where bh->b_bdev is never
set. I hit this BUG while testing the DAX PMD fault path.
Instead, initialize bh.b_bdev before passing bh into get_block(). It is
possible that the filesystem's get_block() will update bh.b_bdev, and this
is fine - we just want to initialize bh.b_bdev to something reasonable so
that the calls to __dax_dbg() work and print something useful.
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 1 +
1 file changed, 1 insertion(+)
diff -puN fs/dax.c~dax-fix-null-pointer-dereference-in-__dax_dbg fs/dax.c
--- a/fs/dax.c~dax-fix-null-pointer-dereference-in-__dax_dbg
+++ a/fs/dax.c
@@ -624,6 +624,7 @@ int __dax_pmd_fault(struct vm_area_struc
}
memset(&bh, 0, sizeof(bh));
+ bh.b_bdev = inode->i_sb->s_bdev;
block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
bh.b_size = PMD_SIZE;
_
Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are
mm-dax-fix-livelock-allow-dax-pmd-mappings-to-become-writeable.patch
dax-fix-null-pointer-dereference-in-__dax_dbg.patch
dax-fix-conversion-of-holes-to-pmds.patch
pmem-add-wb_cache_pmem-to-the-pmem-api.patch
pmem-add-wb_cache_pmem-to-the-pmem-api-v6.patch
dax-support-dirty-dax-entries-in-radix-tree.patch
dax-support-dirty-dax-entries-in-radix-tree-v6.patch
mm-add-find_get_entries_tag.patch
dax-add-support-for-fsync-sync.patch
dax-add-support-for-fsync-sync-v6.patch
dax-add-support-for-fsync-msync-v7.patch
dax-add-support-for-fsync-msync-v8.patch
ext2-call-dax_pfn_mkwrite-for-dax-fsync-msync.patch
ext4-call-dax_pfn_mkwrite-for-dax-fsync-msync.patch
xfs-call-dax_pfn_mkwrite-for-dax-fsync-msync.patch
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