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 B5A08374A08 for ; Thu, 17 Sep 2026 01:39:45 +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=1789609187; cv=none; b=DcfeoYlI+I5L5Y1hP/AmODfBXHwXXeiGFFw4afmj5jiOF4rVHNNyHUY31NeY+E8oasTQVar3f+laLIz7fvxUH+Z/FHFSqdcGHkoNAw61KfEzeEg6Go4cPf/2GVq6GHa2ZIj/bA72ZECg7CzPpgSWK+yA32Fd73ix1wwDD8JtknI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789609187; c=relaxed/simple; bh=4EE5F6H628vu71vyZ2FG3MwVZuXPXbW19bhe86h7iTQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=h/8k4pu/xbWxYuMjrxXylaK3KMImmbMNKcSmpDQJipLEI7m45mrI1RZN5ZeM69bY5TSE1eMbV1tTRK7hrYgYV434kX7owAdj5/dY06egUtvPPELXCdl5JeCSR5jLBY1BgNmnAYD+3AKMP9J8LDIEKn1WaLT+FXGDMROrEow9Kuw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=j+mKp52w; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="j+mKp52w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 135F21F00893; Thu, 17 Sep 2026 01:39:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789609185; bh=y0mlPqB0joid0mBrFQuz8jugi6bvOUJPMU2ZkVT/94o=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=j+mKp52wsmhg0yac7zigbY3o/CROtdbHlZ0NQ5iWZDBs0M5rIT/XuQ5pLf3xEfVTF e5l4FVkXBzys6HFtU3Khpl3OHf7a9WBwx0wLm9r7Zyl7YVInDBs7NAhJQ4LPeaDEDG 3Tq/1KsVMOhVV2UHZcNXxsDOEt1icrKCwjp8Mx1YY8WfKth0zeYaHbA6uGdDAp7ztg Riic7XgCiBPGOFn/TgaM0cWAbPDTfTzCbiiVkNS16RHyPoiaIYgy2830FroJDBXum6 UcIoYY0aqZ86DcyB8o5YYf63CQvCz15KHFLqxfpw/I+0/n4i68We6qOP0kedfakEtV Flkyq0cbLAzAQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Norbert Szetei , =?UTF-8?q?G=C3=BCnther=20Noack?= , =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= , Sasha Levin Subject: [PATCH 6.18.y 5/5] landlock: Fix use-after-free of the source's parent directory Date: Wed, 16 Sep 2026 21:39:40 -0400 Message-ID: <20260917013940.3651217-5-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260917013940.3651217-1-sashal@kernel.org> References: <2026091639-trophy-refract-3155@gregkh> <20260917013940.3651217-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Norbert Szetei [ Upstream commit 2c6dc792538260a8087ac5b22c31b3b8e47c85d6 ] current_check_refer_path() reads old_dentry->d_parent without holding a reference nor a lock on it, and then dereferences it in collect_domain_accesses() and in the audit record. A reference on a child does not pin its parent: __d_move() reassigns dentry->d_parent and drops the reference the child held on its former parent. hook_path_rename() is not affected because the rename path calls lock_rename() before the hook, so the source cannot be reparented under it. hook_path_link() has no such protection: filename_linkat() holds a reference on the source dentry but neither locks nor references its parent, so a concurrent rename(2) can reparent the source while security_path_link() runs, and the former parent can then be removed and freed while the hook walks it. A process can trigger this after entering a Landlock domain that handles at least one filesystem access right. The process can then race a linkat(2) loop against rename(2) and rmdir(2): BUG: KASAN: slab-use-after-free in collect_domain_accesses+0x278/0x290 Read of size 4 at addr ffff888160bd53f4 by task llrepro2/549 collect_domain_accesses+0x278/0x290 current_check_refer_path+0x952/0x1120 security_path_link+0x1be/0x320 filename_linkat+0x342/0x6d0 __x64_sys_linkat+0xfa/0x150 Freed by task 562: kmem_cache_free+0x139/0x4c0 i_callback+0x4b/0x80 rcu_core+0x7dc/0x10a0 Take a reference on the dentry selected as the source parent, using dget() for the common-mount-root case and dget_parent() otherwise. Release it after the hierarchy walk and synchronous audit logging. Cc: stable@vger.kernel.org Fixes: b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER") Signed-off-by: Norbert Szetei Reviewed-by: Günther Noack Tested-by: Günther Noack Link: https://patch.msgid.link/E9CDD9E6-E960-4DE2-B1AC-5667D52ABB3E@doyensec.com [mic: Clarify the caller, reachability, and reference handling] Signed-off-by: Mickaël Salaün Signed-off-by: Sasha Levin --- security/landlock/fs.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/security/landlock/fs.c b/security/landlock/fs.c index a9a5fc5ba1bb8..a32658c18880f 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -1196,11 +1196,12 @@ static int current_check_refer_path(struct dentry *const old_dentry, /* * old_dentry may be the root of the common mount point and * !IS_ROOT(old_dentry) at the same time (e.g. with open_tree() and - * OPEN_TREE_CLONE). We do not need to call dget(old_parent) because - * we keep a reference to old_dentry. + * OPEN_TREE_CLONE). Pin the dentry used as old_parent in either case. + * Otherwise, dget_parent() safely fetches and pins the current parent + * against a concurrent rename(2). */ - old_parent = (old_dentry == mnt_dir.dentry) ? old_dentry : - old_dentry->d_parent; + old_parent = (old_dentry == mnt_dir.dentry) ? dget(old_dentry) : + dget_parent(old_dentry); /* new_dir->dentry is equal to new_dentry->d_parent */ allow_parent1 = collect_domain_accesses(subject->domain, mnt_dir.dentry, @@ -1209,8 +1210,10 @@ static int current_check_refer_path(struct dentry *const old_dentry, allow_parent2 = collect_domain_accesses(subject->domain, mnt_dir.dentry, new_dir->dentry, &layer_masks_parent2); - if (allow_parent1 && allow_parent2) + if (allow_parent1 && allow_parent2) { + dput(old_parent); return 0; + } /* * To be able to compare source and destination domain access rights, @@ -1222,8 +1225,10 @@ static int current_check_refer_path(struct dentry *const old_dentry, subject->domain, &mnt_dir, access_request_parent1, &layer_masks_parent1, &request1, old_dentry, access_request_parent2, &layer_masks_parent2, &request2, - exchange ? new_dentry : NULL)) + exchange ? new_dentry : NULL)) { + dput(old_parent); return 0; + } if (request1.access) { request1.audit.u.path.dentry = old_parent; @@ -1233,6 +1238,7 @@ static int current_check_refer_path(struct dentry *const old_dentry, request2.audit.u.path.dentry = new_dir->dentry; landlock_log_denial(subject, &request2); } + dput(old_parent); /* * This prioritizes EACCES over EXDEV for all actions, including -- 2.53.0