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Btrfs: fix segmentation fault when doing dio read 

Commit 2dabb32484 ("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>
This commit is contained in:
Liu Bo 2017-04-07 13:11:10 -07:00 committed by David Sterba
parent 2e949b0a55
commit 97bf5a5589
1 changed files with 6 additions and 2 deletions
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8
fs/btrfs/inode.c
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@ -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;
}
}