From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:51584 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1162739AbeBOPXr (ORCPT ); Thu, 15 Feb 2018 10:23:47 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Alexander Viro , Andrew Morton , Andrey Konovalov , Cong Wang , Linus Torvalds , Eric Biggers Subject: [PATCH 4.4 070/108] nsfs: mark dentry with DCACHE_RCUACCESS Date: Thu, 15 Feb 2018 16:17:07 +0100 Message-Id: <20180215151232.115260005@linuxfoundation.org> In-Reply-To: <20180215151222.267507937@linuxfoundation.org> References: <20180215151222.267507937@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Cong Wang commit 073c516ff73557a8f7315066856c04b50383ac34 upstream. Andrey reported a use-after-free in __ns_get_path(): spin_lock include/linux/spinlock.h:299 [inline] lockref_get_not_dead+0x19/0x80 lib/lockref.c:179 __ns_get_path+0x197/0x860 fs/nsfs.c:66 open_related_ns+0xda/0x200 fs/nsfs.c:143 sock_ioctl+0x39d/0x440 net/socket.c:1001 vfs_ioctl fs/ioctl.c:45 [inline] do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:685 SYSC_ioctl fs/ioctl.c:700 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691 We are under rcu read lock protection at that point: rcu_read_lock(); d = atomic_long_read(&ns->stashed); if (!d) goto slow; dentry = (struct dentry *)d; if (!lockref_get_not_dead(&dentry->d_lockref)) goto slow; rcu_read_unlock(); but don't use a proper RCU API on the free path, therefore a parallel __d_free() could free it at the same time. We need to mark the stashed dentry with DCACHE_RCUACCESS so that __d_free() will be called after all readers leave RCU. Fixes: e149ed2b805f ("take the targets of /proc/*/ns/* symlinks to separate fs") Cc: Alexander Viro Cc: Andrew Morton Reported-by: Andrey Konovalov Signed-off-by: Cong Wang Signed-off-by: Linus Torvalds Cc: Eric Biggers Signed-off-by: Greg Kroah-Hartman --- fs/nsfs.c | 1 + 1 file changed, 1 insertion(+) --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -95,6 +95,7 @@ slow: return ERR_PTR(-ENOMEM); } d_instantiate(dentry, inode); + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_fsdata = (void *)ns_ops; d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry); if (d) {