CVE-2024-26956: nilfs2: fix failure to detect DAT corruption in btree and direct mappings

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

nilfs2: fix failure to detect DAT corruption in btree and direct mappings

Patch series "nilfs2: fix kernel bug at submitbhwbc()".

This resolves a kernel BUG reported by syzbot. Since there are two flaws involved, I've made each one a separate patch.

The first patch alone resolves the syzbot-reported bug, but I think both fixes should be sent to stable, so I've tagged them as such.

This patch (of 2):

Syzbot has reported a kernel bug in submitbhwbc() when writing file data to a nilfs2 file system whose metadata is corrupted.

There are two flaws involved in this issue.

The first flaw is that when nilfsgetblock() locates a data block using btree or direct mapping, if the disk address translation routine nilfsdattranslate() fails with internal code -ENOENT due to DAT metadata corruption, it can be passed back to nilfsgetblock(). This causes nilfsgetblock() to misidentify an existing block as non-existent, causing both data block lookup and insertion to fail inconsistently.

The second flaw is that nilfsgetblock() returns a successful status in this inconsistent state. This causes the caller blockwritebeginint() or others to request a read even though the buffer is not mapped, resulting in a BUGON check for the BHMapped flag in submitbhwbc() failing.

This fixes the first issue by changing the return value to code -EINVAL when a conversion using DAT fails with code -ENOENT, avoiding the conflicting condition that leads to the kernel bug described above. Here, code -EINVAL indicates that metadata corruption was detected during the block lookup, which will be properly handled as a file system error and converted to -EIO when passing through the nilfs2 bmap layer.