Commit 97bf5a55 authored Apr 07, 2017 by Liu Bo Committed by David Sterba Apr 11, 2017

Btrfs: fix segmentation fault when doing dio read



Commit 2dabb324 ("Btrfs: Direct I/O read: Work on sectorsized blocks")
introduced this bug during iterating bio pages in dio read's endio hook,
and it could end up with segment fault of the dio reading task.

So the reason is 'if (nr_sectors--)', and it makes the code assume that
there is one more block in the same page, so page offset is increased and
the bio which is created to repair the bad block then has an incorrect
bvec.bv_offset, and a later access of the page content would throw a
segmentation fault.

This also adds ASSERT to check page offset against page size.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 2e949b0a

fs/btrfs/inode.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -7972,8 +7972,10 @@ next_block_or_try_again:

		start += sectorsize;

		if (nr_sectors--) {
		nr_sectors--;
		if (nr_sectors) {
		pgoff += sectorsize;
		ASSERT(pgoff < PAGE_SIZE);
		goto next_block_or_try_again;
		}
		}
		@@ -8074,8 +8076,10 @@ next:

		ASSERT(nr_sectors);

		if (--nr_sectors) {
		nr_sectors--;
		if (nr_sectors) {
		pgoff += sectorsize;
		ASSERT(pgoff < PAGE_SIZE);
		goto next_block;
		}
		}

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