Commit eab95db6 authored Jan 22, 2016 by Ross Zwisler Committed by Linus Torvalds Jan 22, 2016

dax: never rely on bh.b_dev being set by get_block()



Previously in DAX we assumed that calls to get_block() would set
bh.b_bdev, and we would then use that value even in error cases for
debugging.  This caused a NULL pointer dereference in __dax_dbg() which
was fixed by a previous commit, but that commit only changed the one
place where we were hitting an error.

Instead, update dax.c so that we always initialize bh.b_bdev as best we
can based on the information that DAX has.  get_block() may or may not
update to a new value, but this at least lets us get something helpful
from bh.b_bdev for error messages and not have to worry about whether it
was set by get_block() or not.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5eb88dca

fs/dax.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -246,6 +246,7 @@ 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;

		if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
		struct address_space *mapping = inode->i_mapping;
		@@ -607,6 +608,7 @@ 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_size = PAGE_SIZE;

		repeat:
		@@ -1078,6 +1080,7 @@ 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_size = PAGE_CACHE_SIZE;
		err = get_block(inode, index, &bh, 0);
		if (err < 0)

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