Re: [Linux-kernel-mentees] [PATCH] net: tipc: fix general protection fault in tipc_conn_delete_sub

[B K Karthik <bkkarthik@pesu.pes.edu>]

On Mon, Jul 27, 2020 at 6:53 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Jul 27, 2020 at 06:40:57PM +0530, B K Karthik wrote:
> > fix a general protection fault in tipc_conn_delete_sub
> > by checking for the existance of con->server.
> > prevent a null-ptr-deref by returning -EINVAL when
> > con->server is NULL
> >
> > general protection fault, probably for non-canonical address 0xdffffc0000000014: 0000 [#1] PREEMPT SMP KASAN
> > KASAN: null-ptr-deref in range [0x00000000000000a0-0x00000000000000a7]
> > CPU: 1 PID: 113 Comm: kworker/u4:3 Not tainted 5.6.0-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Workqueue: tipc_send tipc_conn_send_work
> > RIP: 0010:tipc_conn_delete_sub+0x54/0x440 net/tipc/topsrv.c:231
> > Code: 48 c1 ea 03 80 3c 02 00 0f 85 f0 03 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6b 18 48 8d bd a0 00 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 c0 03 00 00 48 c7 c0 34 0b 8a 8a 4c 8b a5 a0 00
> > RSP: 0018:ffffc900012d7b58 EFLAGS: 00010206
> > RAX: dffffc0000000000 RBX: ffff8880a8269c00 RCX: ffffffff8789ca01
> > RDX: 0000000000000014 RSI: ffffffff8789a059 RDI: 00000000000000a0
> > RBP: 0000000000000000 R08: ffff8880a8d88380 R09: fffffbfff18577a8
> > R10: fffffbfff18577a7 R11: ffffffff8c2bbd3f R12: dffffc0000000000
> > R13: ffff888093d35a18 R14: ffff8880a8269c00 R15: ffff888093d35a00
> > FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 000000000076c000 CR3: 000000009441d000 CR4: 00000000001406e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  tipc_conn_send_to_sock+0x380/0x560 net/tipc/topsrv.c:266
> >  tipc_conn_send_work+0x6f/0x90 net/tipc/topsrv.c:304
> >  process_one_work+0x965/0x16a0 kernel/workqueue.c:2266
> >  worker_thread+0x96/0xe20 kernel/workqueue.c:2412
> >  kthread+0x388/0x470 kernel/kthread.c:268
> >  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> > Modules linked in:
> > ---[ end trace 2c161a84be832606 ]---
> > RIP: 0010:tipc_conn_delete_sub+0x54/0x440 net/tipc/topsrv.c:231
> > Code: 48 c1 ea 03 80 3c 02 00 0f 85 f0 03 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6b 18 48 8d bd a0 00 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 c0 03 00 00 48 c7 c0 34 0b 8a 8a 4c 8b a5 a0 00
> > RSP: 0018:ffffc900012d7b58 EFLAGS: 00010206
> > RAX: dffffc0000000000 RBX: ffff8880a8269c00 RCX: ffffffff8789ca01
> > RDX: 0000000000000014 RSI: ffffffff8789a059 RDI: 00000000000000a0
> > RBP: 0000000000000000 R08: ffff8880a8d88380 R09: fffffbfff18577a8
> > R10: fffffbfff18577a7 R11: ffffffff8c2bbd3f R12: dffffc0000000000
> > R13: ffff888093d35a18 R14: ffff8880a8269c00 R15: ffff888093d35a00
> > FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000020800000 CR3: 0000000091b8e000 CR4: 00000000001406e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >
> > Reported-and-tested-by: syzbot+55a38037455d0351efd3@syzkaller.appspotmail.com
> > Signed-off-by: B K Karthik <bkkarthik@pesu.pes.edu>
> > ---
> >  net/tipc/topsrv.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/net/tipc/topsrv.c b/net/tipc/topsrv.c
> > index 1489cfb941d8..6c8d0c6bb112 100644
> > --- a/net/tipc/topsrv.c
> > +++ b/net/tipc/topsrv.c
> > @@ -255,6 +255,9 @@ static void tipc_conn_send_to_sock(struct tipc_conn *con)
> >       int count = 0;
> >       int ret;
> >
> > +     if (!con->server)
> > +             return -EINVAL;
>
> What is wrong with looking at the srv local variable instead?
>
> And how is server getting set to NULL and this function still being
> called?

tipc_conn_send_work makes a call to connected() which just returns con
&& test_bit(CF_CONNECTED, &con->flags)
maybe we can add this check to the implementation of connection() if
you agree, but I found this solution to be fairly simpler because I'm
not sure where else connected() is being used, and I did not want to
introduce redundant function calls.

Yes we can replace con->server with the local variable srv. Extremely
sorry, I hadn't noticed it earlier.

please let me know if i've wrongly understood any of these.
thanks,

karthik
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