Re: [PATCH v8 1/9] dax: fix NULL pointer dereference in __dax_dbg()
From: Jan Kara <jack@suse.cz>
Date: 2016-01-12 09:34:58
Also in:
linux-ext4, linux-fsdevel, linux-xfs, lkml, nvdimm
On Thu 07-01-16 22:27:51, Ross Zwisler wrote:
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 <redacted> Cc: Dan Williams <redacted>
Looks good. But don't you need to do the same for __dax_fault(), dax_zero_page_range() and similar places passing bh to dax functions? Honza
quoted hunk ↗ jump to hunk
--- fs/dax.c | 1 + 1 file changed, 1 insertion(+)diff --git a/fs/dax.c b/fs/dax.c index 7af8797..513bba5 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;-- 2.5.0
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