nilfs2: fix sanity check of btree level in nilfs_btree_root_broken()

The range check for b-tree level parameter in nilfs_btree_root_broken()
is wrong; it accepts the case of "level == NILFS_BTREE_LEVEL_MAX" even
though the level is limited to values in the range of 0 to
(NILFS_BTREE_LEVEL_MAX - 1).

Since the level parameter is read from storage device and used to index
nilfs_btree_path array whose element count is NILFS_BTREE_LEVEL_MAX, it
can cause memory overrun during btree operations if the boundary value
is set to the level parameter on device.

This fixes the broken sanity check and adds a comment to clarify that
the upper bound NILFS_BTREE_LEVEL_MAX is exclusive.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
index 059f37137f9a..919fd5bb14a8 100644
--- a/fs/nilfs2/btree.c
+++ b/fs/nilfs2/btree.c
@@ -388,7 +388,7 @@ static int nilfs_btree_root_broken(const struct nilfs_btree_node *node,
         nchildren = nilfs_btree_node_get_nchildren(node);
 
         if (unlikely(level < NILFS_BTREE_LEVEL_NODE_MIN ||
-                     level > NILFS_BTREE_LEVEL_MAX ||
+                     level >= NILFS_BTREE_LEVEL_MAX ||
                      nchildren < 0 ||
                      nchildren > NILFS_BTREE_ROOT_NCHILDREN_MAX)) {
                 pr_crit("NILFS: bad btree root (inode number=%lu): level = %d, flags = 0x%x, nchildren = %d\n",