[Devel] Re: [RFC][PATCH] sunrpc: fix oops in rpc_create() when the mount namespace is unshared

[Cedric Le Goater]

Serge E. Hallyn wrote:
> Quoting Cedric Le Goater (clg at fr.ibm.com):
>> On a system with nfs mounts, if a task unshares its mount namespace,
>> a oops can occur when the system is rebooted if the task is the last
>> to unreference the nfs mount. It will try to create a rpc request
>> using utsname() which has been invalidated by free_nsproxy().
>>
>> The patch fixes the issue by using the global init_utsname() but at
>> the same time, it breaks the capability of identifying rpc clients
>> per uts namespace.
>>
>> Any better suggestions ?
> 
> But the utsname gets freed after the mnt_ns, so the analysis seems
> wrong somehow.

yes but switch_task_namespaces() assigns ->nsproxy to NULL. the result
is the same.
 
> I trust addr2line or whatever verified that rpc_create+0x332/0x42f is
> exactly at the call to utsname()?

yes. it points to net/sunrpc/clnt.c:216

	clnt->cl_nodelen = strlen(utsname()->nodename);

Thanks,

C.



> -serge
> 
>> BUG: unable to handle kernel NULL pointer dereference at 00000004
>> IP: [<c024c9ab>] rpc_create+0x332/0x42f
>> Oops: 0000 [#1] DEBUG_PAGEALLOC
>>
>> Pid: 1857, comm: uts-oops Not tainted (2.6.27-rc5-00319-g7686ad5 #4)
>> EIP: 0060:[<c024c9ab>] EFLAGS: 00210287 CPU: 0
>> EIP is at rpc_create+0x332/0x42f
>> EAX: 00000000 EBX: df26adf0 ECX: c0251887 EDX: 00000001
>> ESI: df26ae58 EDI: c02f293c EBP: dda0fc9c ESP: dda0fc2c
>>  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
>> Process uts-oops (pid: 1857, ti=dda0e000 task=dd9a0778 task.ti=dda0e000)
>> Stack: c0104532 dda0fffc dda0fcac dda0e000 dda0e000 dd93b7f0 00000009 c02f2880
>>        df26aefc dda0fc68 c01096b7 00000000 c0266ee0 c039a070 c039a070 dda0fc74
>>        c012ca67 c039a064 dda0fc8c c012cb20 c03daf74 00000011 00000000 c0275c90
>> Call Trace:
>>  [<c0104532>] ? dump_trace+0xc2/0xe2
>>  [<c01096b7>] ? save_stack_trace+0x1c/0x3a
>>  [<c012ca67>] ? save_trace+0x37/0x8c
>>  [<c012cb20>] ? add_lock_to_list+0x64/0x96
>>  [<c0256fc4>] ? rpcb_register_call+0x62/0xbb
>>  [<c02570c8>] ? rpcb_register+0xab/0xb3
>>  [<c0252f4d>] ? svc_register+0xb4/0x128
>>  [<c0253114>] ? svc_destroy+0xec/0x103
>>  [<c02531b2>] ? svc_exit_thread+0x87/0x8d
>>  [<c01a75cd>] ? lockd_down+0x61/0x81
>>  [<c01a577b>] ? nlmclnt_done+0xd/0xf
>>  [<c01941fe>] ? nfs_destroy_server+0x14/0x16
>>  [<c0194328>] ? nfs_free_server+0x4c/0xaa
>>  [<c019a066>] ? nfs_kill_super+0x23/0x27
>>  [<c0158585>] ? deactivate_super+0x3f/0x51
>>  [<c01695d1>] ? mntput_no_expire+0x95/0xb4
>>  [<c016965b>] ? release_mounts+0x6b/0x7a
>>  [<c01696cc>] ? __put_mnt_ns+0x62/0x70
>>  [<c0127501>] ? free_nsproxy+0x25/0x80
>>  [<c012759a>] ? switch_task_namespaces+0x3e/0x43
>>  [<c01275a9>] ? exit_task_namespaces+0xa/0xc
>>  [<c0117fed>] ? do_exit+0x4fd/0x666
>>  [<c01181b3>] ? do_group_exit+0x5d/0x83
>>  [<c011fa8c>] ? get_signal_to_deliver+0x2c8/0x2e0
>>  [<c0102630>] ? do_notify_resume+0x69/0x700
>>  [<c011d85a>] ? do_sigaction+0x134/0x145
>>  [<c0127205>] ? hrtimer_nanosleep+0x8f/0xce
>>  [<c0126d1a>] ? hrtimer_wakeup+0x0/0x1c
>>  [<c0103488>] ? work_notifysig+0x13/0x1b
>>  =======================
>> Code: 70 20 68 cb c1 2c c0 e8 75 4e 01 00 8b 83 ac 00 00 00 59 3d 00 f0 ff ff 5f 77 63 eb 57 a1 00 80 2d c0 8b 80 a8 02 00 00 8d 73 68 <8b> 40 04 83 c0 45 e8 41 46 f7 ff ba 20 00 00 00 83 f8 21 0f 4c
>> EIP: [<c024c9ab>] rpc_create+0x332/0x42f SS:ESP 0068:dda0fc2c
>>
>> Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
>> ---
>>  net/sunrpc/clnt.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
>> index 76739e9..a59cdf4 100644
>> --- a/net/sunrpc/clnt.c
>> +++ b/net/sunrpc/clnt.c
>> @@ -213,10 +213,10 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
>>  	}
>>
>>  	/* save the nodename */
>> -	clnt->cl_nodelen = strlen(utsname()->nodename);
>> +	clnt->cl_nodelen = strlen(init_utsname()->nodename);
>>  	if (clnt->cl_nodelen > UNX_MAXNODENAME)
>>  		clnt->cl_nodelen = UNX_MAXNODENAME;
>> -	memcpy(clnt->cl_nodename, utsname()->nodename, clnt->cl_nodelen);
>> +	memcpy(clnt->cl_nodename, init_utsname()->nodename, clnt->cl_nodelen);
>>  	rpc_register_client(clnt);
>>  	return clnt;
>>
>> -- 
>> 1.5.5.1

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