CVE-2024-47699

In the Linux kernel, the following vulnerability has been resolved:

nilfs2: fix potential null-ptr-deref in nilfs_btree_insert()

Patch series "nilfs2: fix potential issues with empty b-tree nodes".

This series addresses three potential issues with empty b-tree nodes that

can occur with corrupted filesystem images, including one recently

discovered by syzbot.

This patch (of 3):

If a b-tree is broken on the device, and the b-tree height is greater than

2 (the level of the root node is greater than 1) even if the number of

child nodes of the b-tree root is 0, a NULL pointer dereference occurs in

nilfs_btree_prepare_insert(), which is called from nilfs_btree_insert().

This is because, when the number of child nodes of the b-tree root is 0,

nilfs_btree_do_lookup() does not set the block buffer head in any of

path[x].bp_bh, leaving it as the initial value of NULL, but if the level

of the b-tree root node is greater than 1, nilfs_btree_get_nonroot_node(),

which accesses the buffer memory of path[x].bp_bh, is called.

Fix this issue by adding a check to nilfs_btree_root_broken(), which

performs sanity checks when reading the root node from the device, to

detect this inconsistency.

Thanks to Lizhi Xu for trying to solve the bug and clarifying the cause

early on.