Vulnerability CVE-2024-26956
Published: 2024-05-01

Description:
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.

 References:
https://git.kernel.org/stable/c/b67189690eb4b7ecc84ae16fa1e880e0123eaa35
https://git.kernel.org/stable/c/9cbe1ad5f4354f4df1445e5f4883983328cd6d8e
https://git.kernel.org/stable/c/c3b5c5c31e723b568f83d8cafab8629d9d830ffb
https://git.kernel.org/stable/c/2e2619ff5d0def4bb6c2037a32a6eaa28dd95c84
https://git.kernel.org/stable/c/46b832e09d43b394ac0f6d9485d2b1a06593f0b7
https://git.kernel.org/stable/c/f69e81396aea66304d214f175aa371f1b5578862
https://git.kernel.org/stable/c/a8e4d098de1c0f4c5c1f2ed4633a860f0da6d713
https://git.kernel.org/stable/c/82827ca21e7c8a91384c5baa656f78a5adfa4ab4
https://git.kernel.org/stable/c/f2f26b4a84a0ef41791bd2d70861c8eac748f4ba
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