CVE-2026-68450: btrfs: free mapping node on duplicate reloc root insert

From: Greg Kroah-Hartman <[email protected]>

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

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

btrfs: free mapping node on duplicate reloc root insert

__add_reloc_root() allocates a mapping_node before inserting it into
rc->reloc_root_tree.  If rb_simple_insert() finds an existing entry, it
returns the existing rb_node and leaves the newly allocated node unlinked.

The error path then returns -EEXIST without freeing the new node.  Since
the node was never inserted into reloc_root_tree, the later cleanup in
put_reloc_control() cannot find it either.

Free the newly allocated node before returning -EEXIST.

The callers currently assert that -EEXIST should not happen, so this is a
defensive cleanup for an unexpected duplicate insert path.  If the path is
ever reached, the local allocation should still be released.

The Linux kernel CVE team has assigned CVE-2026-68450 to this issue.


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

	Issue introduced in 5.13 with commit 57a304cfd43b2b4a5b44b8f5dc026abb34183068 and fixed in 6.6.148 with commit 92bedc0455552b42ada1a1f42b0e3a8593cdfccc
	Issue introduced in 5.13 with commit 57a304cfd43b2b4a5b44b8f5dc026abb34183068 and fixed in 6.12.101 with commit 14a8be9428435ee17f17fae7991215c246b7fd43
	Issue introduced in 5.13 with commit 57a304cfd43b2b4a5b44b8f5dc026abb34183068 and fixed in 6.18.42 with commit 797dc567146c7e3c4f8d9680e4fbc76e0a6d9151
	Issue introduced in 5.13 with commit 57a304cfd43b2b4a5b44b8f5dc026abb34183068 and fixed in 7.1.6 with commit ae0629ff9ccb836416ada129f4edc7efea6eaaad
	Issue introduced in 5.13 with commit 57a304cfd43b2b4a5b44b8f5dc026abb34183068 and fixed in 7.2-rc5 with commit 6a8269b6459ed870a8156c106a0f597383907872

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-2026-68450
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/92bedc0455552b42ada1a1f42b0e3a8593cdfccc
	https://git.kernel.org/stable/c/14a8be9428435ee17f17fae7991215c246b7fd43
	https://git.kernel.org/stable/c/797dc567146c7e3c4f8d9680e4fbc76e0a6d9151
	https://git.kernel.org/stable/c/ae0629ff9ccb836416ada129f4edc7efea6eaaad
	https://git.kernel.org/stable/c/6a8269b6459ed870a8156c106a0f597383907872