nilfs2: fix slab-out-of-bounds in nilfs_direct_propagate after truncation

Shuangpeng Bai reported that KASAN detected a slab-out-of-bounds error
in nilfs_direct_propagate() during testing.

Analysis revealed that after truncating a file, a node block immediately
below the B-tree root was not deleted.  Instead, it remained in the B-tree
node cache in a dirty state.  The log writer subsequently detected this
block and incorrectly invoked nilfs_direct_propagate() on it, which is
designed to handle only data blocks in direct mapping.

B-tree nodes in the cache are managed by virtual block numbers, and their
logical keys typically exceed the range expected by direct mapping.
Consequently, processing such a node as a direct mapping entry triggers
a slab-out-of-bounds access.

The root cause is that when a B-tree mapping collapses into a direct
mapping during truncation, an intermediate node block pointed to by the
root node is left behind as garbage instead of being explicitly deleted.

This resolves the issue by adding a nilfs_btree_discard() operation
to delete the remaining intermediate node block during the conversion.
A 'deform' flag is added to the bop_delete interface to explicitly signal
that the deletion is part of a mapping transformation.  This allows the
B-tree mapping implementation to perform the necessary cleanup and
discarding of the residual node structure that would be otherwise be left
orphaned after the transition.

Reported-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
Closes: https://lore.kernel.org/r/08A3603A-ADB6-484C-9015-9AC1340E6FB8@gmail.com
Fixes: 36a580eb489f ("nilfs2: direct block mapping")
Cc: stable@vger.kernel.org
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

0 files changed, 0 insertions, 0 deletions