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author | Ross Zwisler <ross.zwisler@linux.intel.com> | 2016-01-22 15:10:31 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-01-22 17:02:18 -0800 |
commit | d4bbe7068b60e9263f08c54e6c2a0166c0f37317 (patch) | |
tree | 2b9f1223bd9742ccffde05d2dfc515231a5afdf5 | |
parent | 2101ae42899a14fe7caa73114e2161e778328661 (diff) | |
download | lwn-d4bbe7068b60e9263f08c54e6c2a0166c0f37317.tar.gz lwn-d4bbe7068b60e9263f08c54e6c2a0166c0f37317.zip |
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@linux.intel.com>
Reported-by: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | fs/dax.c | 1 |
1 files changed, 1 insertions, 0 deletions
@@ -624,6 +624,7 @@ 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; block = (sector_t)pgoff << (PAGE_SHIFT - blkbits); bh.b_size = PMD_SIZE; |