btrfs: zoned: don't clobber the extent buffer when zeroing it out

Summary

In the Linux kernel, the following vulnerability has been resolved: btrfs: zoned: don't clobber the extent buffer when zeroing it out On a zoned filesystem a freed-but-still-dirty tree block is written out as zeros (EXTENT_BUFFER_ZONED_ZEROOUT) only to keep the zone write pointer advancing. btree_csum_one_bio() implemented this by memzeroing the extent buffer's own folios before submission. That destroys the in-memory buffer while it may still be referenced. In particular btrfs_free_tree_block() can run on it afterwards and reads the header to add a delayed reference; once the header has been zeroed it frees bytenr 0 and corrupts the extent tree (the btrfs_header_bytenr(buf) != 0 ASSERT in btrfs_free_tree_block(), or an "unable to find ref" abort). It is flaky and reproduces under fsstress, e.g. generic/461 and generic/013. Write the zeros to disk from the shared zero page instead and leave the extent buffer content untouched, so any later reference - including the delayed reference from btrfs_free_tree_block() - still sees a valid header. end_bbio_meta_write() now clears writeback on the buffer's own folios, as the bio no longer carries them.

Timeline

1. Sep 17, 2026, 4:07 PM UTCCVE published
2. Oct 21, 2026, 12:50 PM UTCRecord last updated

Affected versions

• Linux Linux

  From aa6313e6ff2bfbf736a2739047bba355d8241584 · fixed in efa5084d08030aa557fdefa3e4a73b2501b7d207; From aa6313e6ff2bfbf736a2739047bba355d8241584 · fixed in 92484ad014f2e2b0e0e7bbc1610951e978cf557c; From aa6313e6ff2bfbf736a2739047bba355d8241584 · fixed in 98e3747587f9f87f010d8d7e55786216249a94af; From aa6313e6ff2bfbf736a2739047bba355d8241584 · fixed in db4b9eefc8ee0bcaeee4d5e6a7313905f6a2fe7c

• Linux Linux

  6.8

• KernelLinux

  From 6.8.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.52; From 6.19.0 · fixed in 7.2.6

References 4