From: Ross Zwisler Date: Fri, 22 Jan 2016 23:10:31 +0000 (-0800) Subject: dax: fix NULL pointer dereference in __dax_dbg() X-Git-Tag: v4.5-rc1~12^2~11 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=d4bbe7068b60e9263f08c54e6c2a0166c0f37317;p=linux.git 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 Reported-by: Dan Williams Cc: Jan Kara Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/dax.c b/fs/dax.c index 7af879759064..513bba5f1e02 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -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;