Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752562AbdC1Md3 (ORCPT ); Tue, 28 Mar 2017 08:33:29 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:58850 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751796AbdC1Md1 (ORCPT ); Tue, 28 Mar 2017 08:33:27 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andrey Ulanov , Dmitry Vyukov , "David S. Miller" Subject: [PATCH 4.4 05/76] net: unix: properly re-increment inflight counter of GC discarded candidates Date: Tue, 28 Mar 2017 14:30:02 +0200 Message-Id: <20170328122600.196617326@linuxfoundation.org> X-Mailer: git-send-email 2.12.1 In-Reply-To: <20170328122559.966310440@linuxfoundation.org> References: <20170328122559.966310440@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4686 Lines: 111 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andrey Ulanov [ Upstream commit 7df9c24625b9981779afb8fcdbe2bb4765e61147 ] Dmitry has reported that a BUG_ON() condition in unix_notinflight() may be triggered by a simple code that forwards unix socket in an SCM_RIGHTS message. That is caused by incorrect unix socket GC implementation in unix_gc(). The GC first collects list of candidates, then (a) decrements their "children's" inflight counter, (b) checks which inflight counters are now 0, and then (c) increments all inflight counters back. (a) and (c) are done by calling scan_children() with inc_inflight or dec_inflight as the second argument. Commit 6209344f5a37 ("net: unix: fix inflight counting bug in garbage collector") changed scan_children() such that it no longer considers sockets that do not have UNIX_GC_CANDIDATE flag. It also added a block of code that that unsets this flag _before_ invoking scan_children(, dec_iflight, ). This may lead to incorrect inflight counters for some sockets. This change fixes this bug by changing order of operations: UNIX_GC_CANDIDATE is now unset only after all inflight counters are restored to the original state. kernel BUG at net/unix/garbage.c:149! RIP: 0010:[] [] unix_notinflight+0x3b4/0x490 net/unix/garbage.c:149 Call Trace: [] unix_detach_fds.isra.19+0xff/0x170 net/unix/af_unix.c:1487 [] unix_destruct_scm+0xf9/0x210 net/unix/af_unix.c:1496 [] skb_release_head_state+0x101/0x200 net/core/skbuff.c:655 [] skb_release_all+0x1a/0x60 net/core/skbuff.c:668 [] __kfree_skb+0x1a/0x30 net/core/skbuff.c:684 [] kfree_skb+0x184/0x570 net/core/skbuff.c:705 [] unix_release_sock+0x5b5/0xbd0 net/unix/af_unix.c:559 [] unix_release+0x49/0x90 net/unix/af_unix.c:836 [] sock_release+0x92/0x1f0 net/socket.c:570 [] sock_close+0x1b/0x20 net/socket.c:1017 [] __fput+0x34e/0x910 fs/file_table.c:208 [] ____fput+0x1a/0x20 fs/file_table.c:244 [] task_work_run+0x1a0/0x280 kernel/task_work.c:116 [< inline >] exit_task_work include/linux/task_work.h:21 [] do_exit+0x183a/0x2640 kernel/exit.c:828 [] do_group_exit+0x14e/0x420 kernel/exit.c:931 [] get_signal+0x663/0x1880 kernel/signal.c:2307 [] do_signal+0xc5/0x2190 arch/x86/kernel/signal.c:807 [] exit_to_usermode_loop+0x1ea/0x2d0 arch/x86/entry/common.c:156 [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:190 [] syscall_return_slowpath+0x4d3/0x570 arch/x86/entry/common.c:259 [] entry_SYSCALL_64_fastpath+0xc4/0xc6 Link: https://lkml.org/lkml/2017/3/6/252 Signed-off-by: Andrey Ulanov Reported-by: Dmitry Vyukov Fixes: 6209344 ("net: unix: fix inflight counting bug in garbage collector") Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/unix/garbage.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -146,6 +146,7 @@ void unix_notinflight(struct user_struct if (s) { struct unix_sock *u = unix_sk(s); + BUG_ON(!atomic_long_read(&u->inflight)); BUG_ON(list_empty(&u->link)); if (atomic_long_dec_and_test(&u->inflight)) @@ -341,6 +342,14 @@ void unix_gc(void) } list_del(&cursor); + /* Now gc_candidates contains only garbage. Restore original + * inflight counters for these as well, and remove the skbuffs + * which are creating the cycle(s). + */ + skb_queue_head_init(&hitlist); + list_for_each_entry(u, &gc_candidates, link) + scan_children(&u->sk, inc_inflight, &hitlist); + /* not_cycle_list contains those sockets which do not make up a * cycle. Restore these to the inflight list. */ @@ -350,14 +359,6 @@ void unix_gc(void) list_move_tail(&u->link, &gc_inflight_list); } - /* Now gc_candidates contains only garbage. Restore original - * inflight counters for these as well, and remove the skbuffs - * which are creating the cycle(s). - */ - skb_queue_head_init(&hitlist); - list_for_each_entry(u, &gc_candidates, link) - scan_children(&u->sk, inc_inflight, &hitlist); - spin_unlock(&unix_gc_lock); /* Here we are. Hitlist is filled. Die. */