Agreed, I was just pawing around in that code, and
this patch looks sane and plausible.
Reviewed-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> On May 21, 2018, at 2:28 PM, bfields@xxxxxxxxxxxx wrote:
>
> This looks right, thanks, it's just waiting on testing--the latest
> Fedora update seems to have broken my test rig's krb5 server, hopefully
> I'll get that back up tommorrow.
>
> --b.
>
> On Fri, May 18, 2018 at 05:13:04PM -0400, Dave Wysochanski wrote:
>> There is a 16-byte memory leak inside sunrpc/auth_gss on an nfs server when
>> a client mounts with 'sec=krb5' in a simple mount / umount loop. The leak
>> is seen by either monitoring the kmalloc-16 slab or with kmemleak enabled
>>
>> unreferenced object 0xffff92e6a045f030 (size 16):
>> comm "nfsd", pid 1096, jiffies 4294936658 (age 761.110s)
>> hex dump (first 16 bytes):
>> 2a 86 48 86 f7 12 01 02 02 00 00 00 00 00 00 00 *.H.............
>> backtrace:
>> [<000000004b2b79a7>] gssx_dec_buffer+0x79/0x90 [auth_rpcgss]
>> [<000000002610ac1a>] gssx_dec_accept_sec_context+0x215/0x6dd [auth_rpcgss]
>> [<000000004fd0e81d>] rpcauth_unwrap_resp+0xa9/0xe0 [sunrpc]
>> [<000000002b099233>] call_decode+0x1e9/0x840 [sunrpc]
>> [<00000000954fc846>] __rpc_execute+0x80/0x3f0 [sunrpc]
>> [<00000000c83a961c>] rpc_run_task+0x10d/0x150 [sunrpc]
>> [<000000002c2cdcd2>] rpc_call_sync+0x4d/0xa0 [sunrpc]
>> [<000000000b74eea2>] gssp_accept_sec_context_upcall+0x196/0x470 [auth_rpcgss]
>> [<000000003271273f>] svcauth_gss_proxy_init+0x188/0x520 [auth_rpcgss]
>> [<000000001cf69f01>] svcauth_gss_accept+0x3a6/0xb50 [auth_rpcgss]
>>
>> If you map the above to code you'll see the following call chain
>> gssx_dec_accept_sec_context
>> gssx_dec_ctx (missing from kmemleak output)
>> gssx_dec_buffer(xdr, &ctx->mech)
>>
>> Inside gssx_dec_buffer there is 'kmemdup' where we allocate memory for
>> any gssx_buffer (buf) and store into buf->data. In the above instance,
>> 'buf == &ctx->mech).
>>
>> Further up in the chain in gssp_accept_sec_context_upcall we see ctx->mech
>> is part of a stack variable 'struct gssx_ctx rctxh'. Now later inside
>> gssp_accept_sec_context_upcall after gssp_call, there is a number of
>> memcpy and kfree statements, but there is no kfree(rctxh.mech.data)
>> after the memcpy into data->mech_oid.data.
>>
>> With this patch applied and the same mount / unmount loop, the kmalloc-16
>> slab is stable and kmemleak enabled no longer shows the above backtrace.
>>
>> Signed-off-by: Dave Wysochanski <dwysocha@xxxxxxxxxx>
>> ---
>> net/sunrpc/auth_gss/gss_rpc_upcall.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sunrpc/auth_gss/gss_rpc_upcall.c b/net/sunrpc/auth_gss/gss_rpc_upcall.c
>> index 46b295e..d98e2b6 100644
>> --- a/net/sunrpc/auth_gss/gss_rpc_upcall.c
>> +++ b/net/sunrpc/auth_gss/gss_rpc_upcall.c
>> @@ -298,9 +298,11 @@ int gssp_accept_sec_context_upcall(struct net *net,
>> if (res.context_handle) {
>> data->out_handle = rctxh.exported_context_token;
>> data->mech_oid.len = rctxh.mech.len;
>> - if (rctxh.mech.data)
>> + if (rctxh.mech.data) {
>> memcpy(data->mech_oid.data, rctxh.mech.data,
>> data->mech_oid.len);
>> + kfree(rctxh.mech.data);
>> + }
>> client_name = rctxh.src_name.display_name;
>> }
>>
>> --
>> 1.8.3.1
>>
>> --
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--
Chuck Lever
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