CVE-2024-36027 Information

May 31, 2024 cve

Description

In the Linux kernel the following vulnerability has been resolved:

btrfs: zoned: do not flag ZEROOUT on non-dirty extent buffer

Btrfs clears the content of an extent buffer marked as EXTENT_BUFFER_ZONED_ZEROOUT before the bio submission. This mechanism is introduced to prevent a write hole of an extent buffer which is once allocated marked dirty but turns out unnecessary and cleaned up within one transaction operation.

Currently btrfs_clear_buffer_dirty() marks the extent buffer as EXTENT_BUFFER_ZONED_ZEROOUT and skips the entry function. If this call happens while the buffer is under IO (with the WRITEBACK flag set without the DIRTY flag) we can add the ZEROOUT flag and clear the buffer’s content just before a bio submission. As a result:

  1. it can lead to adding faulty delayed reference item which leads to a FS corrupted (EUCLEAN) error and

  2. it writes out cleared tree node on disk

The former issue is previously discussed in [1]. The corruption happens when it runs a delayed reference update. So on-disk data is safe.

[1] https://lore.kernel.org/linux-btrfs/3f4f2a0ff1a6c818050434288925bdcf3cd719e5.1709124777.git.naohiro.aota@wdc.com/

The latter one can reach on-disk data. But as that node is already processed by btrfs_clear_buffer_dirty() that will be invalidated in the next transaction commit anyway. So the chance of hitting the corruption is relatively small.

Anyway we should skip flagging ZEROOUT on a non-DIRTY extent buffer to keep the content under IO intact.

Reference

https://git.kernel.org/stable/c/f4b994fccbb6f294c4b31a6ca0114b09f7245043 https://git.kernel.org/stable/c/68879386180c0efd5a11e800b0525a01068c9457

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