Dear Bruce,
I would like to ask you to send first two patches to stable@ (rest ones can be skipped)
It fixes CVE-2018-16884
it was broken since 2012, v3.7 when following patch allowed
to execute svc_create_xprt("tcp-bc") in different net namespaces.
Fixes: commit 23c20ecd4475 ("NFS: callback up - users counting cleanup") # 3.7
On 12/24/18 8:03 PM, J. Bruce Fields wrote:
> So you fixed a bug *and* deleted a net 200 lines? Sign me up.
>
> I guess I'll plan to take this through my tree for 4.21. The patches
> look OK to me, I just want to run it through my testing. That make take
> a couple days due to the holidays.
>
> --b.
>
> On Mon, Dec 24, 2018 at 02:44:24PM +0300, Vasily Averin wrote:
>> v4:
>> - re-split,
>> - use direct call of svc_tcp_prep_reply_hdr() in svc_process_common()
>> - removed unused bc_up
>> - removed useless svc_tcp_bc_class and svc_rdma_bc_class
>> - removed unused xpo_prep_reply_hdr
>>
>> v3:
>> - first patch was reworked again,
>> instead of svc_xprt search svc_process_common() now uses
>> bc_prep_reply_hdr() function pointer saved on per-netns sunrpc_net.
>> - first patch was splitted into 5 parts.
>> - comments cleanup
>>
>> v2:
>> - first patch was reworked to satisfy Trond's requirements:
>> to do not assign rqstp->rq_xprt in svc_process_common() at all,
>> provide proper xpt_ops reference as a new parameter,
>> adopt functions potentially called from svc_process_common()
>> to properly handle rqstp->rq_xprt = NULL case.
>>
>>
>> nfsv41+ clients are still not properly net-namespace-filied.
>>
>> OpenVz got report on crash in svc_process_common()
>> abd founf that bc_svc_process() cannot use serv->sv_bc_xprt as a pointer.
>>
>> serv is global structure, but sv_bc_xprt is assigned per-netnamespace.
>> If nfsv41+ shares (with the same minorversion) are mounted in several containers together
>> then bc_svc_process() can use wrong backchannel or even access freed memory.
>>
>> OpenVz got report on crash svc_process_common(),
>> and after careful investigations Evgenii Shatokhin have found its reproducer.
>> Then I've reproduced the problem on last mainline kernel.
>>
>> In described scenario you need to have:
>> - nodeA: VM with 2 interfaces and debug kernel with enabled KASAN.
>> - nodeB: any other node
>> - NFS-SRV: NFSv41+ server (4.2 is used in exaple below)
>>
>> 1) nodeA: mount nfsv41+ share
>> # mount -t nfs4 -o vers=4.2 NFS-SRV:/export/ /mnt/ns1
>> VvS: here serv->sv_bc_xprt is assigned first time,
>> in xs_tcp_bc_up() it is assigned to svc_xprt of mount's backchannel
>>
>> 2) nodeA: create net namespace, and mount the same (or any other) NFSv41+ share
>> # ip netns add second
>> # ip link set ens2 netns second
>> # ip netns exec second bash
>> (inside netns second) # dhclient ens2
>> VvS: now nets got access to external network
>> (inside netns second) # mount -t nfs4 -o vers=4.2 NFS-SRV:/export/ /mnt/ns2
>> VvS: now serv->sv_bc_xprt is overwritten by reference to svc_xprt of new mount's backchannel
>> NB: you can mount any other NFS share but minorversion must be the same.
>> NB2: if hardware allows you can use rdma transport here
>> NB3: you can access nothing in mounted share, problem's trigger was enabled already.
>>
>> 3) NodeA, destroy mount inside netns and then netns itself.
>>
>> (inside netns second) # umount /mnt/ns2
>> (inside netns second) # ip link set ens2 netns 1
>> (inside netns second) # exit
>> VvS: return to init_net
>> # ip netns del second
>> VvS: now second NFS mount and second net namespace was destroyed.
>>
>> 4) Node A: prepare backchannel event
>> # echo test1 > /mnt/ns1/test1.txt
>> # echo test2 > /mnt/ns1/test2.txt
>> # python
>>>>> fl=open('/mnt/ns1/test1.txt','r')
>>>>>
>>
>> 4) Node B: replace file open by NodeA
>> # mount -t nfs -o vers=4.2 NFS-SRV:/export/ /mnt/
>> # mv /mnt/test2.txt /mnt/test1.txt
>>
>> ===> KASAN on nodeA detect an access to already freed memory.
>> (see dmesg example in attach of v1 patch version)
>>
>> svc_process_common()
>> /* Setup reply header */
>> rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(rqstp); <<< HERE
>>
>> svc_process_common() uses already freed rqstp->rq_xprt,
>> it was assigned in bc_svc_process() where it was taken from serv->sv_bc_xprt.
>>
>> serv->sv_bc_xprt cannot be used as a pointer,
>> it can be assigned per net-namespace, either in svc_bc_tcp_create()
>> or in xprt_rdma_bc_up().
>>
>> According to Trond, the whole "let's set up rqstp->rq_xprt
>> for the back channel" is nothing but a giant hack in order
>> to work around the fact that svc_process_common() uses it
>> to find the xpt_ops, and perform a couple of (meaningless
>> for the back channel) tests of xpt_flags.
>>
>> All we really need in svc_process_common() is to be able to run
>> rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr()
>>
>> Bruce J Fields points that this xpo_prep_reply_hdr() call
>> is an awfully roundabout way just to do "svc_putnl(resv, 0);"
>> in the tcp case.
>>
>> To fix the problem svc_process_common() checks svc_rqstp->rq_prot
>> inherited from incoming request and if required calls
>> svc_tcp_prep_reply_hdr() directly.
>>
>> It was also required to store a pointer to struct net in the
>> struct svc_rqst so that functions called from inside
>> svc_process_common() (nfs4_callback_compound(),
>> svcauth_gss_accept() and some other) can find it.
>> Some other functions was adopted to handle empty rqstp->rq_xprt
>>
>> First patch switches svnauth_gss-* function to use SVC_NET()
>> 2nd patch fixes use-after-free itself:
>> to adjust reply header svc_process_common() checks prot of incoming request
>> and if required calls svc_tcp_prep_reply_hdr() directly
>> function called from svc_process_common() are adopted to properly handle
>> rqstp->rq_xprt = NULL
>> 3rd patch replaces sv_bc_xprt use in in svc_is_backchannel()
>> by simple boolean flag
>> 4rd patch removes unused bc_up calls
>>
>> 5th and 6th patches removes unused fake "transports", svc_tcp/rdma_bc_class
>> 7th patch removes unused xpo_prep_reply_hdr callback
>> Rest of patches are minor cleanup.
>>
>> Vasily Averin (10):
>> sunrpc: use SVC_NET() in svcauth_gss_* functions
>> sunrpc: use-after-free in svc_process_common()
>> sunrpc: replace svc_serv->sv_bc_xprt by boolean flag
>> sunrpc: remove unused bc_up operation from rpc_xprt_ops
>> sunrpc: remove svc_tcp_bc_class
>> sunrpc: remove svc_rdma_bc_class
>> sunrpc: remove unused xpo_prep_reply_hdr callback
>> sunrpc: make visible processing error in bc_svc_process()
>> sunrpc: fix debug message in svc_create_xprt()
>> nfs: minor typo in nfs4_callback_up_net()
>>
>> fs/nfs/callback.c | 10 +-
>> include/linux/sunrpc/bc_xprt.h | 10 +-
>> include/linux/sunrpc/svc.h | 7 +-
>> include/linux/sunrpc/svc_rdma.h | 1 -
>> include/linux/sunrpc/svc_xprt.h | 1 -
>> include/linux/sunrpc/xprt.h | 1 -
>> include/trace/events/sunrpc.h | 6 +-
>> net/sunrpc/auth_gss/svcauth_gss.c | 8 +-
>> net/sunrpc/svc.c | 24 +++--
>> net/sunrpc/svc_xprt.c | 9 +-
>> net/sunrpc/svcsock.c | 120 -----------------------
>> net/sunrpc/xprtrdma/backchannel.c | 20 ----
>> net/sunrpc/xprtrdma/svc_rdma.c | 6 --
>> net/sunrpc/xprtrdma/svc_rdma_sendto.c | 4 -
>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 59 -----------
>> net/sunrpc/xprtrdma/transport.c | 1 -
>> net/sunrpc/xprtrdma/xprt_rdma.h | 1 -
>> net/sunrpc/xprtsock.c | 12 ---
>> 18 files changed, 46 insertions(+), 254 deletions(-)
>>
>> --
>> 2.17.1
>
