netdev - Re: dccp: null-pointer dereference on close

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Date:	Tue, 1 Mar 2011 06:59:45 +0100
From:	Gerrit Renker <gerrit@....abdn.ac.uk>
To:	Johan Hovold <jhovold@...il.com>
Cc:	dccp@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: dccp: null-pointer dereference on close

Johan,

thanks a lot for the detailed description.

I think I have found the cause of the dccp timewait problem: in the 
mainline tree there is a path

 dccp_v4_do_rcv() 
	|
	| state other than OPEN
	v
 dccp_rcv_state_process()
	|
	| DCCP_PKT_RESET
	v
 dccp_rcv_reset()
	|
	v
 dccp_time_wait()

In the backtrace dccp_close() had been called, hence dccp_set_state() has
destroyed inet_csk(sk)->icsk_bind_hash, which then subsequently in the
misplaced dccp_time_wait() caused the NULL pointer exception.

I have just checked, this problem seems to not be possible in the test
tree, since it checks first in dccp_rcv_state_process() if DCCP_CLOSED
has been entered (if it receives a packet in this state, it sends a 
Reset with code 3, "No Connection").

I am attaching the relevant patch from the test tree - would it be possible
for you to test it with the same setup? (The relevant passage is right in 
the first hunk, where it tests for state == DCCP_CLOSED).

Will submit this patch subsequently also.

Thanks again,
Gerrit


| root@...ro:~# [84140.128631] ------------[ cut here ]------------
| [84140.133575] WARNING: at net/ipv4/inet_timewait_sock.c:141 __inet_twsk_hashdance+0x48/0x128()
| [84140.142517] Modules linked in: arc4 ecb carl9170 rt2870sta(C) mac80211 r8712u(C) crc_ccitt ah
| [84140.151794] [<c0038850>] (unwind_backtrace+0x0/0xec) from [<c0055364>] (warn_slowpath_common)
| [84140.161743] [<c0055364>] (warn_slowpath_common+0x4c/0x64) from [<c0055398>] (warn_slowpath_n)
| [84140.171966] [<c0055398>] (warn_slowpath_null+0x1c/0x24) from [<c02b72d0>] (__inet_twsk_hashd)
| [84140.182373] [<c02b72d0>] (__inet_twsk_hashdance+0x48/0x128) from [<c031caa0>] (dccp_time_wai)
| [84140.192413] [<c031caa0>] (dccp_time_wait+0x40/0xc8) from [<c031c15c>] (dccp_rcv_state_proces)
| [84140.202636] [<c031c15c>] (dccp_rcv_state_process+0x120/0x538) from [<c032609c>] (dccp_v4_do_)
| [84140.213043] [<c032609c>] (dccp_v4_do_rcv+0x11c/0x14c) from [<c0286594>] (release_sock+0xac/0)
| [84140.222442] [<c0286594>] (release_sock+0xac/0x110) from [<c031fd34>] (dccp_close+0x28c/0x380)
| [84140.231475] [<c031fd34>] (dccp_close+0x28c/0x380) from [<c02d9a78>] (inet_release+0x64/0x70)
| [84140.240386] [<c02d9a78>] (inet_release+0x64/0x70) from [<c0284ddc>] (sock_release+0x24/0xb8)
| [84140.249328] [<c0284ddc>] (sock_release+0x24/0xb8) from [<c0284e94>] (sock_close+0x24/0x34)
| [84140.258087] [<c0284e94>] (sock_close+0x24/0x34) from [<c00c2e4c>] (fput+0x108/0x1f4)
| [84140.266296] [<c00c2e4c>] (fput+0x108/0x1f4) from [<c00c0104>] (filp_close+0x70/0x7c)
| [84140.274505] [<c00c0104>] (filp_close+0x70/0x7c) from [<c00c01c4>] (sys_close+0xb4/0x10c)
| [84140.283081] [<c00c01c4>] (sys_close+0xb4/0x10c) from [<c0033a80>] (ret_fast_syscall+0x0/0x30)
| [84140.292114] ---[ end trace b8877ec9d542c32e ]---
| [84140.296997] Unable to handle kernel NULL pointer dereference at virtual address 00000010


View attachment "DCCP_Reorder-Input-Processing.diff" of type "text/x-diff" (5695 bytes)