On 09/21/2016 04:04 AM, David Sterba wrote:
On Tue, Sep 20, 2016 at 10:57:41AM -0700, Liu Bo wrote:
On Tue, Sep 20, 2016 at 03:16:36PM +0200, David Sterba wrote:
On Wed, Sep 14, 2016 at 05:22:57PM -0700, Liu Bo wrote:
During updating btree, we could push items between sibling
nodes/leaves, for leaves data sections starts reversely from
the end of the block while for nodes we only have key pairs
which are stored one by one from the start of the block.

So we could do try to push key pairs from one node to the next
node right in the tree, and after that, we update the node's
nritems to reflect the correct end while leaving the stale
content in the node.  One may intentionally corrupt the fs
image and access the stale content by bumping the nritems and
causes various crashes.

This takes the in-memory @nritems as the correct one and
gets to memset the unused part of a btree node.

Signed-off-by: Liu Bo <bo.li....@oracle.com>

Reviewed-by: David Sterba <dste...@suse.com>

---
 fs/btrfs/extent_io.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c2325c3..56c9dee 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3732,6 +3732,17 @@ static noinline_for_stack int write_one_eb(struct 
extent_buffer *eb,
        if (btrfs_header_owner(eb) == BTRFS_TREE_LOG_OBJECTID)
                bio_flags = EXTENT_BIO_TREE_LOG;

+       /* set btree node beyond nritems with 0 to avoid stale content */
+       if (btrfs_header_level(eb) > 0) {

We can do the same for leaves.

In theory, the problem also applies for leaves, but I haven't got a
reproducer for leaf case.

So I'll update a v2 with leaf memset, please review that part more
carefully :)

You can keep it a separate patch, this one is fine. I didn't expect to
reproduce a crash with a bogus nritems in a leaf but rather apply the
same on a leaf buffer. The magic formula is (please verify)

start = nr * sizeof(struct btrfs_disk_key);
end = nr ? btrfs_item_offset(eb, btrfs_item_nr(nr - 1)) : eb->len;


This is the start/end of the memset for the leaves? Doesn't look right, since leaves looks like this:

item headers 0,1,2 .. N  -> [ empty space ] <- item data N, ... 2, 1, 0

The empty space is from the end of header N to the start of data N.

-chris
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