CVE-2026-46159: btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-28 · updated 2026-10-15
Weakness: CWE-367

Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak btrfs_ioctl_space_info() has a TOCTOU race between two passes over the block group RAID type lists. The first pass counts entries to determine the allocation size, then the second pass fills the buffer. The groups_sem rwlock is released between passes, allowing concurrent block group removal to reduce the entry count. When the second pass fills fewer entries than the first pass counted, copy_to_user() copies the full alloc_size bytes including trailing uninitialized kmalloc bytes to userspace. Fix by copying only total_spaces entries (the actually-filled count from the second pass) instead of alloc_size bytes, and switch to kzalloc so any future copy size mismatch cannot leak heap data.

Affected products

Linux kernel: from 2.6.34.1 before 6.6.140; from 6.7 before 6.12.90; from 6.13 before 6.18.32; from 6.19 before 7.0.7; 2.6.34, 2.6.34-rc2, 2.6.34-rc3, 2.6.34-rc4, 2.6.34-rc5, 2.6.34-rc6 (+1) — fixed in 6.12.90, 6.18.32, 6.6.140, 7.0.7

How to fix

Upgrade to a fixed version: Linux kernel 6.12.90, 6.18.32, 6.6.140, 7.0.7. Check the vendor advisory for mitigations.

References

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