From mboxrd@z Thu Jan 1 00:00:00 1970 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 ACC8F41D4E9; Sat, 12 Sep 2026 10:00:05 +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=1789207206; cv=none; b=kDdY9d9PdoShS3h38ZoPbhdbZ4YSY+VO1ZD+6pVNUQM1iwgenBBAL1SYZwvobUMe8UM+XpIuaVkjaGKqlwhydWa7HvHomG1qhPdFGJJMDZyi6FT73qrtjUFvHkPJSueRlK0DLdWlEHbV6pwHWXxjTR9gZnakrqabWt/EF+WEZCk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789207206; c=relaxed/simple; bh=ZRkkpc3jN8UA5FOoqt4loEkscQ/2Eb6yhuIJFZ+vgSE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jmzM+loDXSyxUhf8wGotYZfvbjIYRHZryQFC2VGacytHIELlPbx10nL0a14KIyeDduG+iRUvSvuL4+8zMyUq1iFpqM2eHczWGnTsEE9ne8UG7pK4kUp1CdH7GZ33T9hE2BeGE8GPorszZATEEQwb8jqyPC8v/eD15UO9mQ27hb4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=AO8ydFxE; 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="AO8ydFxE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A75BA1F000FF; Sat, 12 Sep 2026 10:00:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789207205; bh=j5OZpllpDGW7FsvaFjhUQE1yvXfcfyQZaD0zMLkjA+M=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=AO8ydFxECSA6ewjAl4WKajpbPPSacMVG8c/2QaQqrWHznVRanmgjQVKUBXd27U3vO lCvTGfedwtP+pYOvqM6+UEC4fYiTFiHHTqSNCtvLBrV6ZQmTDHqk3sYSuoH5tjwPM9 1JJhQZaZUeecMu8DD//xo16hWYHwajTArWsnx/N4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sashiko , Reinette Chatre , "Borislav Petkov (AMD)" , Ben Horgan , Tony Luck , Sasha Levin Subject: [PATCH 6.18 0363/1518] fs/resctrl: Prevent use-after-free in rdtgroup_kn_put() Date: Sat, 12 Sep 2026 08:42:12 +0200 Message-ID: <20260912065631.682354305@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065623.398859879@linuxfoundation.org> References: <20260912065623.398859879@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: Reinette Chatre [ Upstream commit f5bcf539484d2d604c2f2330e09487ea090b21c7 ] A struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that need the structure to remain valid across a sleep (while waiting on acquiring rdtgroup_mutex) take a reference with rdtgroup_kn_get() and release it with rdtgroup_kn_put(). The release path is intended to serve as the fallback freer: if the count drops to zero and the group has already been marked RDT_DELETED, rdtgroup_kn_put() frees the structure. The bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub() resulting from a resctrl directory remove or resctrl fs unmount act as the primary freer: they hold rdtgroup_mutex and free each rdtgroup whose waitcount is zero, otherwise they set RDT_DELETED and leave the freeing to the last waiter. These two freers race. rdtgroup_kn_put() commits waitcount == 0 with atomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags. Between those two operations a concurrent caller of free_all_child_rdtgrp() or rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via atomic_read(), call rdtgroup_remove(), and kfree() the structure. The subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then a use-after-free, and the structure may even be freed twice if the freed memory happens to satisfy the RDT_DELETED flag check. Replace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock() so that the decrement-to-zero takes rdtgroup_mutex before the count becomes globally visible. The inspection of rdtgroup::flags then runs under the same mutex held by the bulk freers, making the two paths mutually exclusive. The common case where the count does not reach zero remains lock-free. Defer kernfs_unbreak_active_protection() until after the mutex is dropped since kernfs active protections functionally wrap rdtgroup_mutex. Remove resource group, which in turn drops its kernfs reference, after kernfs protection is restored. [ bp: Split the commit messsages into smaller, easier-parseable paragraphs. ] Fixes: b8511ccc75c0 ("x86/resctrl: Fix use-after-free when deleting resource groups") Closes: https://sashiko.dev/#/patchset/20260515193944.15114-1-tony.luck%40intel.com?part=1 Reported-by: Sashiko Assisted-by: GitHub_Copilot:gemini-3.1-pro Signed-off-by: Reinette Chatre Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Ben Horgan Reviewed-by: Tony Luck Link: https://patch.msgid.link/8d028bbea582dc382a4cc166b235f75bd5901aea.1783963505.git.reinette.chatre@intel.com Signed-off-by: Sasha Levin --- fs/resctrl/rdtgroup.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c index 08e26c0c9fb9c..1f81bd6711551 100644 --- a/fs/resctrl/rdtgroup.c +++ b/fs/resctrl/rdtgroup.c @@ -2528,15 +2528,24 @@ static void rdtgroup_kn_get(struct rdtgroup *rdtgrp, struct kernfs_node *kn) static void rdtgroup_kn_put(struct rdtgroup *rdtgrp, struct kernfs_node *kn) { - if (atomic_dec_and_test(&rdtgrp->waitcount) && - (rdtgrp->flags & RDT_DELETED)) { + bool needs_free; + + if (!atomic_dec_and_mutex_lock(&rdtgrp->waitcount, &rdtgroup_mutex)) { + kernfs_unbreak_active_protection(kn); + return; + } + + needs_free = rdtgrp->flags & RDT_DELETED; + + mutex_unlock(&rdtgroup_mutex); + + kernfs_unbreak_active_protection(kn); + + if (needs_free) { if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP || rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) rdtgroup_pseudo_lock_remove(rdtgrp); - kernfs_unbreak_active_protection(kn); rdtgroup_remove(rdtgrp); - } else { - kernfs_unbreak_active_protection(kn); } } -- 2.53.0