Re: [PATCH v4 02/10] sunrpc: use-after-free in svc_process_common()

J. Bruce Fields
2018-12-24T16:59:32Z

On Mon, Dec 24, 2018 at 02:44:52PM +0300, Vasily Averin wrote:
> 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>
> ---
> include/linux/sunrpc/svc.h | 5 ++++-
> include/trace/events/sunrpc.h | 6 ++++--
> net/sunrpc/svc.c | 9 +++++----
> net/sunrpc/svc_xprt.c | 5 +++--
> net/sunrpc/svcsock.c | 2 +-
> 5 files changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index 73e130a840ce..fdb6b317d974 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -295,9 +295,12 @@ 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
> 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 d13e05f1a990..fb647bc01fc5 100644
> --- a/net/sunrpc/svc.c
> +++ b/net/sunrpc/svc.c
> @@ -1172,7 +1172,8 @@ 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_prot == IPPROTO_TCP)
> + svc_tcp_prep_reply_hdr(rqstp);

svc_tcp_prep_reply_hdr is a one-liner, I'd just copy the svc_putnl() and
comment here.

--b.

>
> svc_putu32(resv, rqstp->rq_xid);
>
> @@ -1244,7 +1245,7 @@ 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 +1337,7 @@ 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;
> @@ -1459,10 +1460,10 @@ 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;
> + 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);
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 51d36230b6e3..bd42da287c26 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -468,10 +468,11 @@ 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;
>
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 986f3ed7d1a2..793149ba1bda 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -1173,7 +1173,7 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp)
> /*
> * Setup response header. TCP has a 4B record length field.
> */
> -static void svc_tcp_prep_reply_hdr(struct svc_rqst *rqstp)
> +void svc_tcp_prep_reply_hdr(struct svc_rqst *rqstp)
> {
> struct kvec *resv = &rqstp->rq_res.head[0];
>
> --
> 2.17.1