Description

In the Linux kernel, the following vulnerability has been resolved: ext4: don't cache extent during splitting extent Caching extents during the splitting process is risky, as it may result in stale extents remaining in the status tree. Moreover, in most cases, the corresponding extent block entries are likely already cached before the split happens, making caching here not particularly useful. Assume we have an unwritten extent, and then DIO writes the first half. [UUUUUUUUUUUUUUUU] on-disk extent U: unwritten extent [UUUUUUUUUUUUUUUU] extent status tree |<- ->| ----> dio write this range First, when ext4_split_extent_at() splits this extent, it truncates the existing extent and then inserts a new one. During this process, this extent status entry may be shrunk, and calls to ext4_find_extent() and ext4_cache_extents() may occur, which could potentially insert the truncated range as a hole into the extent status tree. After the split is completed, this hole is not replaced with the correct status. [UUUUUUU|UUUUUUUU] on-disk extent U: unwritten extent [UUUUUUU|HHHHHHHH] extent status tree H: hole Then, the outer calling functions will not correct this remaining hole extent either. Finally, if we perform a delayed buffer write on this latter part, it will re-insert the delayed extent and cause an error in space accounting. In adition, if the unwritten extent cache is not shrunk during the splitting, ext4_cache_extents() also conflicts with existing extents when caching extents. In the future, we will add checks when caching extents, which will trigger a warning. Therefore, Do not cache extents that are being split.

Affected Products 7

References 8

• git.kernel.org https://git.kernel.org/stable/c/4c2d9dac4d328244f9365b0a1fa27ec802821820
  Patch
• git.kernel.org https://git.kernel.org/stable/c/5b1f4290453314e11cd8e15c7baa8a9b76c19b23
  Patch
• git.kernel.org https://git.kernel.org/stable/c/692103feca376ae4298c92aa8828015d20f1d87b
  Patch
• git.kernel.org https://git.kernel.org/stable/c/8302b5b4aacdbb378f7b1216bb2ee782b5142415
  Patch
• git.kernel.org https://git.kernel.org/stable/c/8b4b19a2f96348d70bfa306ef7d4a13b0bcbea79
  Patch
• git.kernel.org https://git.kernel.org/stable/c/93b2ebbbcb2e63cfc21a1946dfe91d3aa7952036
  Patch
• git.kernel.org https://git.kernel.org/stable/c/96007fd3c106aea773c1afae2d6f64cceb6da208
  Patch
• git.kernel.org https://git.kernel.org/stable/c/9a2b95cdaf07785e2739199037bd9c0863ccc1be
  Patch

Remediation

• git.kernel.org https://git.kernel.org/stable/c/4c2d9dac4d328244f9365b0a1fa27ec802821820
  Patch
• git.kernel.org https://git.kernel.org/stable/c/5b1f4290453314e11cd8e15c7baa8a9b76c19b23
  Patch
• git.kernel.org https://git.kernel.org/stable/c/692103feca376ae4298c92aa8828015d20f1d87b
  Patch
• git.kernel.org https://git.kernel.org/stable/c/8302b5b4aacdbb378f7b1216bb2ee782b5142415
  Patch
• git.kernel.org https://git.kernel.org/stable/c/8b4b19a2f96348d70bfa306ef7d4a13b0bcbea79
  Patch
• git.kernel.org https://git.kernel.org/stable/c/93b2ebbbcb2e63cfc21a1946dfe91d3aa7952036
  Patch
• git.kernel.org https://git.kernel.org/stable/c/96007fd3c106aea773c1afae2d6f64cceb6da208
  Patch
• git.kernel.org https://git.kernel.org/stable/c/9a2b95cdaf07785e2739199037bd9c0863ccc1be
  Patch