From: Vasily Averin <vvs@virtuozzo.com>
Date: Mon, 24 Dec 2018 14:44:52 +0300
Subject: [PATCH] sunrpc: use-after-free in svc_process_common()
Git-commit: d4b09acf924b84bae77cad090a9d108e70b43643
Patch-mainline: v5.0-rc1
References: bsc#1119946 CVE-2018-16884
if node have NFSv41+ mounts inside several net namespaces
it can lead to use-after-free in svc_process_common()
svc_process_common()
/* Setup reply header */
rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(rqstp); <<< HERE
svc_process_common() can use incorrect rqstp->rq_xprt,
its caller function bc_svc_process() takes it from serv->sv_bc_xprt.
The problem is that serv is global structure but sv_bc_xprt
is assigned per-netnamespace.
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.
This patch does not initialiuze rqstp->rq_xprt in bc_svc_process(),
now it calls svc_process_common() with rqstp->rq_xprt = NULL.
To adjust reply header svc_process_common() just check
rqstp->rq_prot and calls svc_tcp_prep_reply_hdr() for tcp case.
To handle rqstp->rq_xprt = NULL case in functions called from
svc_process_common() patch intruduces net namespace pointer
svc_rqst->rq_bc_net and adjust SVC_NET() definition.
Some other function was also adopted to properly handle described case.
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: NeilBrown <neilb@suse.com>
---
include/linux/sunrpc/svc.h | 5 ++++-
net/sunrpc/svc.c | 13 +++++++++----
net/sunrpc/svc_xprt.c | 5 +++--
3 files changed, 16 insertions(+), 7 deletions(-)
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -291,9 +291,12 @@ struct svc_rqst {
struct svc_cacherep * rq_cacherep; /* cache info */
struct task_struct *rq_task; /* service thread */
spinlock_t rq_lock; /* per-request lock */
+ struct net *rq_bc_net; /* pointer to backchannel's
+ * net namespace
+ */
};
-#define SVC_NET(svc_rqst) (svc_rqst->rq_xprt->xpt_net)
+#define SVC_NET(rqst) (rqst->rq_xprt ? rqst->rq_xprt->xpt_net : rqst->rq_bc_net)
/*
* Rigorous type checking on sockaddr type conversions
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1173,7 +1173,12 @@ svc_process_common(struct svc_rqst *rqst
clear_bit(RQ_DROPME, &rqstp->rq_flags);
/* Setup reply header */
- rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(rqstp);
+ if (rqstp->rq_prot == IPPROTO_TCP) {
+ struct kvec *resv = &rqstp->rq_res.head[0];
+
+ /* tcp needs a space for the record length... */
+ svc_putnl(resv, 0);
+ }
svc_putu32(resv, rqstp->rq_xid);
@@ -1245,7 +1250,7 @@ svc_process_common(struct svc_rqst *rqst
* for lower versions. RPC_PROG_MISMATCH seems to be the closest
* fit.
*/
- if (versp->vs_need_cong_ctrl &&
+ if (versp->vs_need_cong_ctrl && rqstp->rq_xprt &&
!test_bit(XPT_CONG_CTRL, &rqstp->rq_xprt->xpt_flags))
goto err_bad_vers;
@@ -1334,7 +1339,7 @@ svc_process_common(struct svc_rqst *rqst
return 0;
close:
- if (test_bit(XPT_TEMP, &rqstp->rq_xprt->xpt_flags))
+ if (rqstp->rq_xprt && test_bit(XPT_TEMP, &rqstp->rq_xprt->xpt_flags))
svc_close_xprt(rqstp->rq_xprt);
dprintk("svc: svc_process close\n");
return 0;
@@ -1461,10 +1466,10 @@ bc_svc_process(struct svc_serv *serv, st
dprintk("svc: %s(%p)\n", __func__, req);
/* Build the svc_rqst used by the common processing routine */
- rqstp->rq_xprt = serv->sv_bc_xprt;
rqstp->rq_xid = req->rq_xid;
rqstp->rq_prot = req->rq_xprt->prot;
rqstp->rq_server = serv;
+ rqstp->rq_bc_net = req->rq_xprt->xprt_net;
rqstp->rq_addrlen = sizeof(req->rq_xprt->addr);
memcpy(&rqstp->rq_addr, &req->rq_xprt->addr, rqstp->rq_addrlen);
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -510,10 +510,11 @@ out:
*/
void svc_reserve(struct svc_rqst *rqstp, int space)
{
+ struct svc_xprt *xprt = rqstp->rq_xprt;
+
space += rqstp->rq_res.head[0].iov_len;
- if (space < rqstp->rq_reserved) {
- struct svc_xprt *xprt = rqstp->rq_xprt;
+ if (xprt && space < rqstp->rq_reserved) {
atomic_sub((rqstp->rq_reserved - space), &xprt->xpt_reserved);
rqstp->rq_reserved = space;