linux-kernel - [PATCH v3 2/2] sunrpc: add a slot to rqstp->rq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20251009-rq_bvec-v3-2-57181360b9cb@kernel.org>
Date: Thu, 09 Oct 2025 10:40:11 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Chuck Lever <chuck.lever@...cle.com>, NeilBrown <neil@...wn.name>, 
 Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>, 
 Tom Talpey <tom@...pey.com>, Trond Myklebust <trondmy@...nel.org>, 
 Anna Schumaker <anna@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 David Howells <dhowells@...hat.com>
Cc: Brandon Adams <brandona@...a.com>, linux-nfs@...r.kernel.org, 
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Jeff Layton <jlayton@...nel.org>
Subject: [PATCH v3 2/2] sunrpc: add a slot to rqstp->rq_bvec for TCP record
 marker

We've seen some occurrences of messages like this in dmesg on some knfsd
servers:

    xdr_buf_to_bvec: bio_vec array overflow

Usually followed by messages like this that indicate a short send (note
that this message is from an older kernel and the amount that it reports
attempting to send is short by 4 bytes):

    rpc-srv/tcp: nfsd: sent 1048155 when sending 1048152 bytes - shutting down socket

svc_tcp_sendmsg() steals a slot in the rq_bvec array for the TCP record
marker. If the send is an unaligned READ call though, then there may not
be enough slots in the rq_bvec array in some cases.

Add a rqstp->rq_bvec_len field and use that to keep track of the length
of rq_bvec. Use that in place of rq_maxpages where it's iterating over
the bvec.

Fixes: e18e157bb5c8 ("SUNRPC: Send RPC message on TCP with a single sock_sendmsg() call")
Tested-by: Brandon Adams <brandona@...a.com>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/nfsd/vfs.c              | 6 +++---
 include/linux/sunrpc/svc.h | 1 +
 net/sunrpc/svc.c           | 4 +++-
 net/sunrpc/svcsock.c       | 4 ++--
 4 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 77f6879c2e063fa79865100bbc2d1e64eb332f42..6c7224570d2dadae21876e0069e0b2e0551af0fa 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1111,7 +1111,7 @@ nfsd_direct_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	v = 0;
 	total = dio_end - dio_start;
-	while (total && v < rqstp->rq_maxpages &&
+	while (total && v < rqstp->rq_bvec_len &&
 	       rqstp->rq_next_page < rqstp->rq_page_end) {
 		len = min_t(size_t, total, PAGE_SIZE);
 		bvec_set_page(&rqstp->rq_bvec[v], *rqstp->rq_next_page,
@@ -1200,7 +1200,7 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	v = 0;
 	total = *count;
-	while (total && v < rqstp->rq_maxpages &&
+	while (total && v < rqstp->rq_bvec_len &&
 	       rqstp->rq_next_page < rqstp->rq_page_end) {
 		len = min_t(size_t, total, PAGE_SIZE - base);
 		bvec_set_page(&rqstp->rq_bvec[v], *rqstp->rq_next_page,
@@ -1318,7 +1318,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (stable && !fhp->fh_use_wgather)
 		kiocb.ki_flags |= IOCB_DSYNC;
 
-	nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
+	nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_bvec_len, payload);
 	iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
 	since = READ_ONCE(file->f_wb_err);
 	if (verf)
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 5506d20857c318774cd223272d4b0022cc19ffb8..0ee1f411860e55d5e0131c29766540f673193d5f 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -206,6 +206,7 @@ struct svc_rqst {
 
 	struct folio_batch	rq_fbatch;
 	struct bio_vec		*rq_bvec;
+	u32			rq_bvec_len;
 
 	__be32			rq_xid;		/* transmission id */
 	u32			rq_prog;	/* program number */
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 4704dce7284eccc9e2bc64cf22947666facfa86a..a6bdd83fba77b13f973da66a1bac00050ae922fe 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -706,7 +706,9 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
 	if (!svc_init_buffer(rqstp, serv, node))
 		goto out_enomem;
 
-	rqstp->rq_bvec = kcalloc_node(rqstp->rq_maxpages,
+	/* +1 for the TCP record marker */
+	rqstp->rq_bvec_len = rqstp->rq_maxpages + 1;
+	rqstp->rq_bvec = kcalloc_node(rqstp->rq_bvec_len,
 				      sizeof(struct bio_vec),
 				      GFP_KERNEL, node);
 	if (!rqstp->rq_bvec)
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 377fcaaaa061463fc5c85fc09c7a8eab5e06af77..2075ddec250b3fdb36becca4a53f1c0536f8634a 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -740,7 +740,7 @@ static int svc_udp_sendto(struct svc_rqst *rqstp)
 	if (svc_xprt_is_dead(xprt))
 		goto out_notconn;
 
-	count = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, xdr);
+	count = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_bvec_len, xdr);
 
 	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec,
 		      count, rqstp->rq_res.len);
@@ -1244,7 +1244,7 @@ static int svc_tcp_sendmsg(struct svc_sock *svsk, struct svc_rqst *rqstp,
 	memcpy(buf, &marker, sizeof(marker));
 	bvec_set_virt(rqstp->rq_bvec, buf, sizeof(marker));
 
-	count = xdr_buf_to_bvec(rqstp->rq_bvec + 1, rqstp->rq_maxpages - 1,
+	count = xdr_buf_to_bvec(rqstp->rq_bvec + 1, rqstp->rq_bvec_len - 1,
 				&rqstp->rq_res);
 
 	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec,

-- 
2.51.0