From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2346EC41513 for ; Thu, 12 Oct 2023 21:55:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347413AbjJLVzV (ORCPT ); Thu, 12 Oct 2023 17:55:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43030 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344165AbjJLVzV (ORCPT ); Thu, 12 Oct 2023 17:55:21 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DAF75B8; Thu, 12 Oct 2023 14:55:18 -0700 (PDT) Received: by linux.microsoft.com (Postfix, from userid 1180) id 3E83F20B74C0; Thu, 12 Oct 2023 14:55:18 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 3E83F20B74C0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1697147718; bh=X9TXOYTeReXKeqvHtc+Vad8+a4hTXFQ9YgHArM9yVNE=; h=Date:From:To:Cc:Subject:From; b=pTSbVjMJnZvDc7zYeEGTsgQiuu3ZE3xRwZ7ix9shTVTzVA6YcRSVk+XLq+ng3ZPtf KaFKy/BmUb43ww/sqcgkY5F4Zi7aRP/1mYNauIL02UtdgD3lX6c//qGEvPDvzEisv3 BE3KlS3nq/U6JDEx8aRQQjXWNiyN8prhXskalI50= Date: Thu, 12 Oct 2023 14:55:18 -0700 From: Dan Clash To: audit@vger.kernel.org, io-uring@vger.kernel.org Cc: linux-kernel@vger.kernel.org, paul@paul-moore.com, axboe@kernel.dk, linux-fsdevel@vger.kernel.org, brauner@kernel.org, dan.clash@microsoft.com Subject: [PATCH] audit,io_uring: io_uring openat triggers audit reference count underflow Message-ID: <20231012215518.GA4048@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org An io_uring openat operation can update an audit reference count from multiple threads resulting in the call trace below. A call to io_uring_submit() with a single openat op with a flag of IOSQE_ASYNC results in the following reference count updates. These first part of the system call performs two increments that do not race. do_syscall_64() __do_sys_io_uring_enter() io_submit_sqes() io_openat_prep() __io_openat_prep() getname() getname_flags() /* update 1 (increment) */ __audit_getname() /* update 2 (increment) */ The openat op is queued to an io_uring worker thread which starts the opportunity for a race. The system call exit performs one decrement. do_syscall_64() syscall_exit_to_user_mode() syscall_exit_to_user_mode_prepare() __audit_syscall_exit() audit_reset_context() putname() /* update 3 (decrement) */ The io_uring worker thread performs one increment and two decrements. These updates can race with the system call decrement. io_wqe_worker() io_worker_handle_work() io_wq_submit_work() io_issue_sqe() io_openat() io_openat2() do_filp_open() path_openat() __audit_inode() /* update 4 (increment) */ putname() /* update 5 (decrement) */ __audit_uring_exit() audit_reset_context() putname() /* update 6 (decrement) */ The fix is to change the refcnt member of struct audit_names from int to atomic_t. kernel BUG at fs/namei.c:262! Call Trace: ... ? putname+0x68/0x70 audit_reset_context.part.0.constprop.0+0xe1/0x300 __audit_uring_exit+0xda/0x1c0 io_issue_sqe+0x1f3/0x450 ? lock_timer_base+0x3b/0xd0 io_wq_submit_work+0x8d/0x2b0 ? __try_to_del_timer_sync+0x67/0xa0 io_worker_handle_work+0x17c/0x2b0 io_wqe_worker+0x10a/0x350 Cc: Link: https://lore.kernel.org/lkml/MW2PR2101MB1033FFF044A258F84AEAA584F1C9A@MW2PR2101MB1033.namprd21.prod.outlook.com/ Fixes: 5bd2182d58e9 ("audit,io_uring,io-wq: add some basic audit support to io_uring") Signed-off-by: Dan Clash --- fs/namei.c | 9 +++++---- include/linux/fs.h | 2 +- kernel/auditsc.c | 8 ++++---- 3 files changed, 10 insertions(+), 9 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 567ee547492b..94565bd7e73f 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -188,7 +188,7 @@ getname_flags(const char __user *filename, int flags, int *empty) } } - result->refcnt = 1; + atomic_set(&result->refcnt, 1); /* The empty path is special. */ if (unlikely(!len)) { if (empty) @@ -249,7 +249,7 @@ getname_kernel(const char * filename) memcpy((char *)result->name, filename, len); result->uptr = NULL; result->aname = NULL; - result->refcnt = 1; + atomic_set(&result->refcnt, 1); audit_getname(result); return result; @@ -261,9 +261,10 @@ void putname(struct filename *name) if (IS_ERR(name)) return; - BUG_ON(name->refcnt <= 0); + if (WARN_ON_ONCE(!atomic_read(&name->refcnt))) + return; - if (--name->refcnt > 0) + if (!atomic_dec_and_test(&name->refcnt)) return; if (name->name != name->iname) { diff --git a/include/linux/fs.h b/include/linux/fs.h index 4aeb3fa11927..85653ce30d2c 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2444,7 +2444,7 @@ struct audit_names; struct filename { const char *name; /* pointer to actual string */ const __user char *uptr; /* original userland pointer */ - int refcnt; + atomic_t refcnt; struct audit_names *aname; const char iname[]; }; diff --git a/kernel/auditsc.c b/kernel/auditsc.c index 21d2fa815e78..6f0d6fb6523f 100644 --- a/kernel/auditsc.c +++ b/kernel/auditsc.c @@ -2212,7 +2212,7 @@ __audit_reusename(const __user char *uptr) if (!n->name) continue; if (n->name->uptr == uptr) { - n->name->refcnt++; + atomic_inc(&n->name->refcnt); return n->name; } } @@ -2241,7 +2241,7 @@ void __audit_getname(struct filename *name) n->name = name; n->name_len = AUDIT_NAME_FULL; name->aname = n; - name->refcnt++; + atomic_inc(&name->refcnt); } static inline int audit_copy_fcaps(struct audit_names *name, @@ -2373,7 +2373,7 @@ void __audit_inode(struct filename *name, const struct dentry *dentry, return; if (name) { n->name = name; - name->refcnt++; + atomic_inc(&name->refcnt); } out: @@ -2500,7 +2500,7 @@ void __audit_inode_child(struct inode *parent, if (found_parent) { found_child->name = found_parent->name; found_child->name_len = AUDIT_NAME_FULL; - found_child->name->refcnt++; + atomic_inc(&found_child->name->refcnt); } } base-commit: 0bb80ecc33a8fb5a682236443c1e740d5c917d1d -- 2.34.1