CVE-2024-26956

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 submit_bh_wbc()”. 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
submit_bh_wbc() 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 nilfs_get_block() locates a data block using btree
or direct mapping, if the disk address translation routine
nilfs_dat_translate() fails with internal code -ENOENT due to DAT metadata
corruption, it can be passed back to nilfs_get_block(). This causes
nilfs_get_block() to misidentify an existing block as non-existent, causing
both data block lookup and insertion to fail inconsistently. The second
flaw is that nilfs_get_block() returns a successful status in this
inconsistent state. This causes the caller __block_write_begin_int() or
others to request a read even though the buffer is not mapped, resulting in
a BUG_ON check for the BH_Mapped flag in submit_bh_wbc() 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.