Bug 2482527 (CVE-2026-46159)

Summary:	CVE-2026-46159 kernel: btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the btrfs filesystem within the Linux kernel. A Time-of-check to time-of-use (TOCTOU) race condition in the `btrfs_ioctl_space_info()` function allows a local attacker to exploit a timing window. This occurs when the system counts entries for allocation size and then fills a buffer, but a concurrent operation reduces the entry count between these two steps. Consequently, uninitialized kernel memory may be copied to userspace, leading to information disclosure.	Story Points:	---
Clone Of:		Environment:
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Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-05-28 11:01:43 UTC

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.

Comment 1 Keith Grant 2026-05-28 15:47:12 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052824-CVE-2026-46159-2689@gregkh/T