CVE-2026-89645: btrfs: drop recovered reloc root refs on recovery failure

CVE-2026-89645: btrfs: drop recovered reloc root refs on recovery failure

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

btrfs: drop recovered reloc root refs on recovery failure

During relocation recovery, each fs root gets a reference to its relocation
root. If loading or adding a later root fails, or if the first transaction
commit fails, btrfs_recover_relocation() jumps to out_unset before
merge_reloc_roots() and clean_dirty_subvols().

put_reloc_control() drops the list-owned relocation root references, but it
does not clear fs_root->reloc_root or drop the references owned by those
pointers. Mount cleanup only drops them when BTRFS_FS_ERROR is set, so an
error such as -ENOMEM while processing a later root can leave references
behind.

Keep temporary references to the fs roots associated during recovery. On
failure, clear their reloc_root pointers and drop the corresponding
references. Once the first transaction commit succeeds, drop only the
temporary fs root references and let the normal merge and cleanup paths
handle the relocation roots.

Fault injection on a pending-relocation image confirmed the cleanup gap.
With an injected first-commit failure, 25 fs roots had reloc_root set with
fs_error=0. With this fix, the same failure path drops that count to 0
before mount fails.

The Linux kernel CVE team has assigned CVE-2026-89645 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.7 with commit f44deb7442edf42abee6be25fca7e3e86061b4c9 and fixed in 6.12.109 with commit 2256d6dc5b88841a8a8b4fd9a9f04730705fb6fd
	Issue introduced in 5.7 with commit f44deb7442edf42abee6be25fca7e3e86061b4c9 and fixed in 6.18.50 with commit 8a64baeb5bbb706b83d2235c1e39f5b77183817f
	Issue introduced in 5.7 with commit f44deb7442edf42abee6be25fca7e3e86061b4c9 and fixed in 7.2.4 with commit 4d43107e807bcd92621106b07f5011411c6341a8
	Issue introduced in 5.7 with commit f44deb7442edf42abee6be25fca7e3e86061b4c9 and fixed in 7.3-rc1 with commit 6d8ba4572922e336f0b59a80751b018e1e135164

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89645
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/btrfs/relocation.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/2256d6dc5b88841a8a8b4fd9a9f04730705fb6fd
	https://git.kernel.org/stable/c/8a64baeb5bbb706b83d2235c1e39f5b77183817f
	https://git.kernel.org/stable/c/4d43107e807bcd92621106b07f5011411c6341a8
	https://git.kernel.org/stable/c/6d8ba4572922e336f0b59a80751b018e1e135164