From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1511988557.16595.25.camel@gmail.com> Subject: Re: KASAN: use-after-free Read in sock_release From: Eric Dumazet To: Cong Wang , syzbot Cc: David Miller , LKML , Linux Kernel Network Developers , syzkaller-bugs@googlegroups.com, linux-fsdevel , Linus Torvalds , Al Viro Date: Wed, 29 Nov 2017 12:49:17 -0800 In-Reply-To: References: <94eb2c19e756c0119b055f1afbd0@google.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2017-11-29 at 11:37 -0800, Cong Wang wrote: > (Cc'ing fs people...) > > On Wed, Nov 29, 2017 at 12:33 AM, syzbot > om> > wrote: > > Hello, > > > > syzkaller hit the following crash on > > 1d3b78bbc6e983fabb3fbf91b76339bf66e4a12c > > git://git.kernel.org/pub/scm/linux/kernel/git/davem/net- > > next.git/master > > compiler: gcc (GCC) 7.1.1 20170620 > > .config is attached > > Raw console output is attached. > > > > Unfortunately, I don't have any reproducer for this bug yet. > > > > > > device syz3 left promiscuous mode > > device syz3 entered promiscuous mode > > ================================================================== > > BUG: KASAN: use-after-free in sock_release+0x1c6/0x1e0 > > net/socket.c:601 > > Read of size 8 at addr ffff8801c8dd1d10 by task syz-executor4/31085 > > > > CPU: 0 PID: 31085 Comm: syz-executor4 Not tainted 4.14.0+ #129 > > Hardware name: Google Google Compute Engine/Google Compute Engine, > > BIOS > > Google 01/01/2011 > > Call Trace: > >  __dump_stack lib/dump_stack.c:17 [inline] > >  dump_stack+0x194/0x257 lib/dump_stack.c:53 > >  print_address_description+0x73/0x250 mm/kasan/report.c:252 > >  kasan_report_error mm/kasan/report.c:351 [inline] > >  kasan_report+0x25b/0x340 mm/kasan/report.c:409 > >  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430 > >  sock_release+0x1c6/0x1e0 net/socket.c:601 > >  sock_close+0x16/0x20 net/socket.c:1125 > >  __fput+0x333/0x7f0 fs/file_table.c:210 > >  ____fput+0x15/0x20 fs/file_table.c:244 > >  task_work_run+0x199/0x270 kernel/task_work.c:113 > >  exit_task_work include/linux/task_work.h:22 [inline] > >  do_exit+0x9bb/0x1ae0 kernel/exit.c:865 > >  do_group_exit+0x149/0x400 kernel/exit.c:968 > >  get_signal+0x73f/0x16c0 kernel/signal.c:2335 > >  do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:809 > >  exit_to_usermode_loop+0x214/0x310 arch/x86/entry/common.c:158 > >  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline] > >  syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264 > >  entry_SYSCALL_64_fastpath+0x94/0x96 > > RIP: 0033:0x452879 > > RSP: 002b:00007fb1c2435ce8 EFLAGS: 00000246 ORIG_RAX: > > 00000000000000ca > > RAX: fffffffffffffe00 RBX: 0000000000758100 RCX: 0000000000452879 > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000758100 > > RBP: 0000000000758100 R08: 0000000000000304 R09: 00000000007580d8 > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > > R13: 0000000000a6f7ff R14: 00007fb1c24369c0 R15: 000000000000000e > > > > Allocated by task 31066: > >  save_stack+0x43/0xd0 mm/kasan/kasan.c:447 > >  set_track mm/kasan/kasan.c:459 [inline] > >  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551 > >  kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3613 > >  kmalloc include/linux/slab.h:499 [inline] > >  sock_alloc_inode+0xb4/0x300 net/socket.c:253 > >  alloc_inode+0x65/0x180 fs/inode.c:208 > >  new_inode_pseudo+0x69/0x190 fs/inode.c:890 > >  sock_alloc+0x41/0x270 net/socket.c:565 > >  __sock_create+0x148/0x850 net/socket.c:1225 > >  sock_create net/socket.c:1301 [inline] > >  SYSC_socket net/socket.c:1331 [inline] > >  SyS_socket+0xeb/0x200 net/socket.c:1311 > >  entry_SYSCALL_64_fastpath+0x1f/0x96 > > > > Freed by task 3039: > >  save_stack+0x43/0xd0 mm/kasan/kasan.c:447 > >  set_track mm/kasan/kasan.c:459 [inline] > >  kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524 > >  __cache_free mm/slab.c:3491 [inline] > >  kfree+0xca/0x250 mm/slab.c:3806 > >  __rcu_reclaim kernel/rcu/rcu.h:190 [inline] > >  rcu_do_batch kernel/rcu/tree.c:2758 [inline] > >  invoke_rcu_callbacks kernel/rcu/tree.c:3012 [inline] > >  __rcu_process_callbacks kernel/rcu/tree.c:2979 [inline] > >  rcu_process_callbacks+0xe79/0x17d0 kernel/rcu/tree.c:2996 > >  __do_softirq+0x29d/0xbb2 kernel/softirq.c:285 > > This looks more like a fs issue than network, my fs knowledge > is not good enough to justify why the hell the inode could be > destroyed before we release the fd. > > My _guess_ is that it is because we defer the ____fput() to a > task work. If this is the case, then fs layer is not guilty for this. > > On the other hand, if we have to blame net layer, it does look > suspicious on the RCU usage in sock_release() where we > claim RCU protection but I don't see we hold any RCU lock > there. There is rcu protection for sock->wq, and the 1 in rcu_dereference_protected(sock->wq, 1) is because we do not have a lockdep convenient way to express that we are the last user of sock, and about to free it. > Also, the code that deferences sock->wq is pretty much > useless now, at least I don't see it catches any bug though. > > > diff --git a/net/socket.c b/net/socket.c > index 42d8e9c9ccd5..b2390b5591a9 100644 > --- a/net/socket.c > +++ b/net/socket.c > @@ -598,9 +598,6 @@ void sock_release(struct socket *sock) >                 module_put(owner); >         } > > -       if (rcu_dereference_protected(sock->wq, 1)->fasync_list) > -               pr_err("%s: fasync list not empty!\n", __func__); > - > At this point, sock->wq must be valid, and freed later (by us) This really looks like some other bug, and a late effect.