[PATCH v3 4/8] sunrpc: use-after-free in svc_process_common()

Vasily Averin
2018-12-21T17:35:44Z

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 already freed rqstp->rq_xprt,
it was assigned in bc_svc_process() where it was taken from serv->sv_bc_xprt.
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 removes rqstp->rq_xprt set up in bc_svc_process(),
now it calls svc_process_common() with rqstp->rq_xprt = NULL.

Patch adjust SVC_NET() definition and adopt function called
from svc_process_common() to proprly handle this situation.

To adjust reply header patch calls bc_reply_hdr() function pointer
saved on per-netns sunrpc_net structure.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
include/linux/sunrpc/svc.h | 2 +-
include/trace/events/sunrpc.h | 6 ++++--
net/sunrpc/svc.c | 17 ++++++++++++-----
net/sunrpc/svc_xprt.c | 5 +++--
4 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 23e33f8f0507..670596f4fdf7 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -300,7 +300,7 @@ struct svc_rqst {
*/
};

-#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
*/
diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 28e384186c35..8617f4fd6b70 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -569,7 +569,8 @@ TRACE_EVENT(svc_process,
__field(u32, vers)
__field(u32, proc)
__string(service, name)
- __string(addr, rqst->rq_xprt->xpt_remotebuf)
+ __string(addr, rqst->rq_xprt ?
+ rqst->rq_xprt->xpt_remotebuf : "(null)")
),

TP_fast_assign(
@@ -577,7 +578,8 @@ TRACE_EVENT(svc_process,
__entry->vers = rqst->rq_vers;
__entry->proc = rqst->rq_proc;
__assign_str(service, name);
- __assign_str(addr, rqst->rq_xprt->xpt_remotebuf);
+ __assign_str(addr, rqst->rq_xprt ?
+ rqst->rq_xprt->xpt_remotebuf : "(null)");
),

TP_printk("addr=%s xid=0x%08x service=%s vers=%u proc=%u",
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 94a2a85c078b..4cf0f0776179 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -30,6 +30,8 @@

#include <trace/events/sunrpc.h>

+#include "netns.h"
+
#define RPCDBG_FACILITY RPCDBG_SVCDSP

static void svc_unregister(const struct svc_serv *serv, struct net *net);
@@ -1153,6 +1155,7 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
struct svc_program *progp;
const struct svc_version *versp = NULL; /* compiler food */
const struct svc_procedure *procp = NULL;
+ struct sunrpc_net *sn;
struct svc_serv *serv = rqstp->rq_server;
__be32 *statp;
u32 prog, vers, proc;
@@ -1172,8 +1175,13 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
clear_bit(RQ_DROPME, &rqstp->rq_flags);

/* Setup reply header */
- rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(rqstp);
-
+ if (rqstp->rq_xprt)
+ rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(rqstp);
+ else {
+ sn = net_generic(SVC_NET(rqstp), sunrpc_net_id);
+ if (sn->bc_prep_reply_hdr)
+ sn->bc_prep_reply_hdr(rqstp);
+ }
svc_putu32(resv, rqstp->rq_xid);

vers = svc_getnl(argv);
@@ -1244,7 +1252,7 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
* 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;

@@ -1336,7 +1344,7 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
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;
@@ -1459,7 +1467,6 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
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;
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 2ffeecfa0978..728ccd4d4490 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -473,10 +473,11 @@ static struct svc_xprt *svc_xprt_dequeue(struct svc_pool *pool)
*/
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;

--
2.17.1