From patchwork Mon Mar 15 17:48:13 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 401107 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF769C4332E for ; Mon, 15 Mar 2021 17:49:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA50264F19 for ; Mon, 15 Mar 2021 17:49:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231837AbhCORtI (ORCPT ); Mon, 15 Mar 2021 13:49:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:44196 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235612AbhCORsm (ORCPT ); Mon, 15 Mar 2021 13:48:42 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8E48A64F2F; Mon, 15 Mar 2021 17:48:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1615830493; bh=vhPAhW0x7mGVQ83LazsE9LXinn6+EdNYgfTVcwbp1ko=; h=Date:From:To:Subject:From; b=MQLqKWSMsoZP/5fi5fg0kpdx9MLx1VT/8eHcRonoWAfxm4LggSGMATNw515nVWs66 bsd+C12CvLq17vN6SpVkVRH12rrS3hxFtM6lWMSOdW1ihZaSG6hiXClhqxKlsJOjCk 69c7dedVuU7R171K+PzbTUfzFpfqjLCbeVRHPtdk= Date: Mon, 15 Mar 2021 10:48:13 -0700 From: akpm@linux-foundation.org To: deller@gmx.de, liorribak@gmail.com, mm-commits@vger.kernel.org, stable@vger.kernel.org, viro@zeniv.linux.org.uk Subject: [merged] binfmt_misc-fix-possible-deadlock-in-bm_register_write.patch removed from -mm tree Message-ID: <20210315174813.ieDvNISHG%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: binfmt_misc: fix possible deadlock in bm_register_write has been removed from the -mm tree. Its filename was binfmt_misc-fix-possible-deadlock-in-bm_register_write.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Lior Ribak Subject: binfmt_misc: fix possible deadlock in bm_register_write There is a deadlock in bm_register_write: First, in the begining of the function, a lock is taken on the binfmt_misc root inode with inode_lock(d_inode(root)). Then, if the user used the MISC_FMT_OPEN_FILE flag, the function will call open_exec on the user-provided interpreter. open_exec will call a path lookup, and if the path lookup process includes the root of binfmt_misc, it will try to take a shared lock on its inode again, but it is already locked, and the code will get stuck in a deadlock To reproduce the bug: $ echo ":iiiii:E::ii::/proc/sys/fs/binfmt_misc/bla:F" > /proc/sys/fs/binfmt_misc/register backtrace of where the lock occurs (#5): 0 schedule () at ./arch/x86/include/asm/current.h:15 1 0xffffffff81b51237 in rwsem_down_read_slowpath (sem=0xffff888003b202e0, count=, state=state@entry=2) at kernel/locking/rwsem.c:992 2 0xffffffff81b5150a in __down_read_common (state=2, sem=) at kernel/locking/rwsem.c:1213 3 __down_read (sem=) at kernel/locking/rwsem.c:1222 4 down_read (sem=) at kernel/locking/rwsem.c:1355 5 0xffffffff811ee22a in inode_lock_shared (inode=) at ./include/linux/fs.h:783 6 open_last_lookups (op=0xffffc9000022fe34, file=0xffff888004098600, nd=0xffffc9000022fd10) at fs/namei.c:3177 7 path_openat (nd=nd@entry=0xffffc9000022fd10, op=op@entry=0xffffc9000022fe34, flags=flags@entry=65) at fs/namei.c:3366 8 0xffffffff811efe1c in do_filp_open (dfd=, pathname=pathname@entry=0xffff8880031b9000, op=op@entry=0xffffc9000022fe34) at fs/namei.c:3396 9 0xffffffff811e493f in do_open_execat (fd=fd@entry=-100, name=name@entry=0xffff8880031b9000, flags=, flags@entry=0) at fs/exec.c:913 10 0xffffffff811e4a92 in open_exec (name=) at fs/exec.c:948 11 0xffffffff8124aa84 in bm_register_write (file=, buffer=, count=19, ppos=) at fs/binfmt_misc.c:682 12 0xffffffff811decd2 in vfs_write (file=file@entry=0xffff888004098500, buf=buf@entry=0xa758d0 ":iiiii:E::ii::i:CF ", count=count@entry=19, pos=pos@entry=0xffffc9000022ff10) at fs/read_write.c:603 13 0xffffffff811defda in ksys_write (fd=, buf=0xa758d0 ":iiiii:E::ii::i:CF ", count=19) at fs/read_write.c:658 14 0xffffffff81b49813 in do_syscall_64 (nr=, regs=0xffffc9000022ff58) at arch/x86/entry/common.c:46 15 0xffffffff81c0007c in entry_SYSCALL_64 () at arch/x86/entry/entry_64.S:120 To solve the issue, the open_exec call is moved to before the write lock is taken by bm_register_write Link: https://lkml.kernel.org/r/20210228224414.95962-1-liorribak@gmail.com Fixes: 948b701a607f1 ("binfmt_misc: add persistent opened binary handler for containers") Signed-off-by: Lior Ribak Acked-by: Helge Deller Cc: Al Viro Cc: Signed-off-by: Andrew Morton --- fs/binfmt_misc.c | 29 ++++++++++++++--------------- 1 file changed, 14 insertions(+), 15 deletions(-) --- a/fs/binfmt_misc.c~binfmt_misc-fix-possible-deadlock-in-bm_register_write +++ a/fs/binfmt_misc.c @@ -649,12 +649,24 @@ static ssize_t bm_register_write(struct struct super_block *sb = file_inode(file)->i_sb; struct dentry *root = sb->s_root, *dentry; int err = 0; + struct file *f = NULL; e = create_entry(buffer, count); if (IS_ERR(e)) return PTR_ERR(e); + if (e->flags & MISC_FMT_OPEN_FILE) { + f = open_exec(e->interpreter); + if (IS_ERR(f)) { + pr_notice("register: failed to install interpreter file %s\n", + e->interpreter); + kfree(e); + return PTR_ERR(f); + } + e->interp_file = f; + } + inode_lock(d_inode(root)); dentry = lookup_one_len(e->name, root, strlen(e->name)); err = PTR_ERR(dentry); @@ -678,21 +690,6 @@ static ssize_t bm_register_write(struct goto out2; } - if (e->flags & MISC_FMT_OPEN_FILE) { - struct file *f; - - f = open_exec(e->interpreter); - if (IS_ERR(f)) { - err = PTR_ERR(f); - pr_notice("register: failed to install interpreter file %s\n", e->interpreter); - simple_release_fs(&bm_mnt, &entry_count); - iput(inode); - inode = NULL; - goto out2; - } - e->interp_file = f; - } - e->dentry = dget(dentry); inode->i_private = e; inode->i_fop = &bm_entry_operations; @@ -709,6 +706,8 @@ out: inode_unlock(d_inode(root)); if (err) { + if (f) + filp_close(f, NULL); kfree(e); return err; }