Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 680BE37FF7F; Thu, 20 Aug 2026 15:16:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787238970; cv=none; b=TgIPHj+WFaaGyfiUbB4bZxy93mSLCB+p0ZodJsdEloYn+s4QQXmbaQgTDD40FKpi0erZudj4yJorBde46aWu0WACuPhGfIaDVBSGDSsaGa+cDVJRjqwRgz+sYnWFKUGNY7/BFWA+r8TCaRTn71ST44T4A2XzAMF8XVhv3P0V4DA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787238970; c=relaxed/simple; bh=2kpK/wGH0Un7avsbQ2fXxAHqH+CtEk1vSQ2WyCp/L+c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qzM0d8ZBII0yPlQIAmHpUGnQel9rKlAYkJCYN/yuF9XbJ1xVD2dnk9QnEf1JO8Nrw24d0rJ9xGVtAIqUSLI89esIutTQPnF7rOTdzExd77a0IwFH5LS9k5yd2d/G6hgDDkMgMXR29w4sDc2X+k3Iv5AW5rbDulmSXuzlt7XAQFk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=M6zZG3VA; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="M6zZG3VA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7BFC11F000E9; Thu, 20 Aug 2026 15:16:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1787238969; bh=4OMp7DCLf2eF1OAwNkTrbs/imcBy2c0c/PFLpbUeAnA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=M6zZG3VACNy8W2ig0x35hSYgIsyUqk3d7skCW2R/ltWyHtNVb4/MvwJBWaQcz+Yf4 xaQwQMoIhg0GO40jl+duzHvImisK02YaWXI72fJ0ziJJ8XexL8trkqVs6/wdW6RCMF IGuEDHHXMgsYltUveuhr02reijbaNc6bOFJ10/Ug= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Weiming Shi , Xiang Mei , "Darrick J. Wong" , Christoph Hellwig , Carlos Maiolino Subject: [PATCH 6.18 104/217] xfs: fix off-by-one in rtrefcount btree root level validation Date: Thu, 20 Aug 2026 16:54:32 +0200 Message-ID: <20260820145240.872768514@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260820145237.531699751@linuxfoundation.org> References: <20260820145237.531699751@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Xiang Mei commit cc3144da377de5fb422d44a2311f978623f7c900 upstream. xfs_rtrefcountbt_compute_maxlevels() sets mp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1; where the trailing "+ 1" already accounts for the inode-root level, so the deepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must satisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels). The two on-disk validation paths, xfs_rtrefcountbt_verify() and xfs_iformat_rtrefcount(), check the root level with ">" instead of ">=", so a crafted rtreflink (metadir + realtime + reflink) image whose /rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on mount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1, exceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is sized for exactly bc_maxlevels entries, the first btree op on such a cursor indexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is reached by the first rtrefcount cursor built after mount, via log/CoW recovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an FS_IOC_GETFSMAP over the realtime device. Reject a root level equal to m_rtrefc_maxlevels, matching the ">=" form already used by the sibling data-device refcount/rmap verifiers and the in-memory rtrmap verifier. BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101) Write of size 2 at addr ffff888018391658 by task exploit/144 xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101) xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308) xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113) xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085) xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551) xfs_mountfs (fs/xfs/xfs_mount.c:1158) xfs_fs_fill_super (fs/xfs/xfs_super.c:1940) get_tree_bdev_flags (fs/super.c:1634) vfs_get_tree (fs/super.c:1694) path_mount (fs/namespace.c:4161) __x64_sys_mount (fs/namespace.c:4367) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216 The buggy address is located 8 bytes to the right of allocated 216-byte region [ffff888018391578, ffff888018391650) Kernel panic - not syncing: Fatal exception Cc: stable@vger.kernel.org # v6.14 Fixes: 9abe03a0e4f978 ("xfs: introduce realtime refcount btree ondisk definitions") Reported-by: Weiming Shi Signed-off-by: Xiang Mei Reviewed-by: "Darrick J. Wong" Reviewed-by: Christoph Hellwig Signed-off-by: Carlos Maiolino Signed-off-by: Greg Kroah-Hartman --- fs/xfs/libxfs/xfs_rtrefcount_btree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/fs/xfs/libxfs/xfs_rtrefcount_btree.c +++ b/fs/xfs/libxfs/xfs_rtrefcount_btree.c @@ -201,7 +201,7 @@ xfs_rtrefcountbt_verify( if (fa) return fa; level = be16_to_cpu(block->bb_level); - if (level > mp->m_rtrefc_maxlevels) + if (level >= mp->m_rtrefc_maxlevels) return __this_address; return xfs_btree_fsblock_verify(bp, mp->m_rtrefc_mxr[level != 0]); @@ -651,7 +651,7 @@ xfs_iformat_rtrefcount( numrecs = be16_to_cpu(dfp->bb_numrecs); level = be16_to_cpu(dfp->bb_level); - if (level > mp->m_rtrefc_maxlevels || + if (level >= mp->m_rtrefc_maxlevels || xfs_rtrefcount_droot_space_calc(level, numrecs) > dsize) { xfs_inode_mark_sick(ip, XFS_SICK_INO_CORE); return -EFSCORRUPTED;