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.

Link: https://lkml.kernel.org/r/20240313105827.5296-1-konishi.ryusuke@gmail.com
Link: https://lkml.kernel.org/r/20240313105827.5296-2-konishi.ryusuke@gmail.com


Fixes: c3a7abf0 ("nilfs2: support contiguous lookup of blocks")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by:  <syzbot+cfed5b56649bddf80d6e@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=cfed5b56649bddf80d6e


Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>