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, Ive 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 Ive 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.

Affected Software

References

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