Revert "NFSD: Remove the cap on number of operations per NFSv4 COMPOUND"

I've found that pynfs COMP6 now leaves the connection or lease in a
strange state, which causes CLOSE9 to hang indefinitely. I've dug
into it a little, but I haven't been able to root-cause it yet.
However, I bisected to commit 48aab16 ("NFSD: Remove the cap on
number of operations per NFSv4 COMPOUND").

Tianshuo Han also reports a potential vulnerability when decoding
an NFSv4 COMPOUND. An attacker can place an arbitrarily large op
count in the COMPOUND header, which results in:

[   51.410584] nfsd: vmalloc error: size 1209533382144, exceeds total
pages, mode:0xdc0(GFP_KERNEL|__GFP_ZERO),
nodemask=(null),cpuset=/,mems_allowed=0

when NFSD attempts to allocate the COMPOUND op array.

Let's restore the operation-per-COMPOUND limit, but increased to 200
for now.

Reported-by: tianshuo han <hantianshuo233@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Cc: stable@vger.kernel.org
Tested-by: Tianshuo Han <hantianshuo233@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: chucklever

fs/nfsd/nfs4proc.c

@@ -2893,10 +2893,20 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 
 	rqstp->rq_lease_breaker = (void **)&cstate->clp;
 
-	trace_nfsd_compound(rqstp, args->tag, args->taglen, args->opcnt);
+	trace_nfsd_compound(rqstp, args->tag, args->taglen, args->client_opcnt);
 	while (!status && resp->opcnt < args->opcnt) {
 		op = &args->ops[resp->opcnt++];
 
+		if (unlikely(resp->opcnt == NFSD_MAX_OPS_PER_COMPOUND)) {
+			/* If there are still more operations to process,
+			 * stop here and report NFS4ERR_RESOURCE. */
+			if (cstate->minorversion == 0 &&
+			    args->client_opcnt > resp->opcnt) {
+				op->status = nfserr_resource;
+				goto encode_op;
+			}
+		}
+
 		/*
 		 * The XDR decode routines may have pre-set op->status;
 		 * for example, if there is a miscellaneous XDR error
@@ -2973,7 +2983,7 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 			status = op->status;
 		}
 
-		trace_nfsd_compound_status(args->opcnt, resp->opcnt,
+		trace_nfsd_compound_status(args->client_opcnt, resp->opcnt,
 					   status, nfsd4_op_name(op->opnum));
 
 		nfsd4_cstate_clear_replay(cstate);

fs/nfsd/nfs4state.c

@@ -3902,6 +3902,7 @@ static __be32 check_forechannel_attrs(struct nfsd4_channel_attrs *ca, struct nfs
 	ca->headerpadsz = 0;
 	ca->maxreq_sz = min_t(u32, ca->maxreq_sz, maxrpc);
 	ca->maxresp_sz = min_t(u32, ca->maxresp_sz, maxrpc);
+	ca->maxops = min_t(u32, ca->maxops, NFSD_MAX_OPS_PER_COMPOUND);
 	ca->maxresp_cached = min_t(u32, ca->maxresp_cached,
 			NFSD_SLOT_CACHE_SIZE + NFSD_MIN_HDR_SEQ_SZ);
 	ca->maxreqs = min_t(u32, ca->maxreqs, NFSD_MAX_SLOTS_PER_SESSION);

fs/nfsd/nfs4xdr.c

@@ -2488,8 +2488,10 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp)
 
 	if (xdr_stream_decode_u32(argp->xdr, &argp->minorversion) < 0)
 		return false;
-	if (xdr_stream_decode_u32(argp->xdr, &argp->opcnt) < 0)
+	if (xdr_stream_decode_u32(argp->xdr, &argp->client_opcnt) < 0)
 		return false;
+	argp->opcnt = min_t(u32, argp->client_opcnt,
+			    NFSD_MAX_OPS_PER_COMPOUND);
 
 	if (argp->opcnt > ARRAY_SIZE(argp->iops)) {
 		argp->ops = vcalloc(argp->opcnt, sizeof(*argp->ops));

fs/nfsd/nfsd.h

@@ -57,6 +57,9 @@ struct readdir_cd {
 	__be32			err;	/* 0, nfserr, or nfserr_eof */
 };
 
+/* Maximum number of operations per session compound */
+#define NFSD_MAX_OPS_PER_COMPOUND	200
+
 struct nfsd_genl_rqstp {
 	struct sockaddr		rq_daddr;
 	struct sockaddr		rq_saddr;

fs/nfsd/xdr4.h

@@ -903,6 +903,7 @@ struct nfsd4_compoundargs {
 	char *				tag;
 	u32				taglen;
 	u32				minorversion;
+	u32				client_opcnt;
 	u32				opcnt;
 	bool				splice_ok;
 	struct nfsd4_op			*ops;