fs: btrfs: Fix tree traversal with btrfs_next_slot()

When traversing slots in a btree (via btrfs_path) with btrfs_next_slot(),
we didn't correctly identify that the last slot in the leaf was reached
and we should jump to the next leaf.

This could lead to any kind of runtime errors or corruptions, like:
* file data not being read at all, or is read partially
* file is read but is corrupted
* (any) metadata being corrupted or not read at all, etc

The easiest way to reproduce this is to read a large enough file that
its EXTENT_DATA items don't fit into a single leaf.

Signed-off-by: Yevgeny Popovych <yevgenyp@pointgrab.com>
Cc: Marek Behun <marek.behun@nic.cz>
Tested-by: Marek Behún <marek.behun@nic.cz>

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 18b47d92fe5f089b2fb3f44b4ddefb9c3fc429dc..d248d79932753f3e7e2d9bd9e32554309b7403dc 100644 (file)
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -272,7 +272,7 @@ int btrfs_next_slot(struct btrfs_path *p)
 {
        struct btrfs_leaf *leaf = &p->nodes[0]->leaf;
 
-       if (p->slots[0] >= leaf->header.nritems)
+       if (p->slots[0] + 1 >= leaf->header.nritems)
                return jump_leaf(p, 1);
 
        p->slots[0]++;