[PATCH v2] NFSD: trim reads past NFS_OFFSET_MAX and fix NFSv3 check

[Dan Aloni <dan.aloni@vastdata.com>]

Due to change in client 8cfb9015280d ("NFS: Always provide aligned
buffers to the RPC read layers"), a read of 0xfff is aligned up to
server rsize of 0x0fff.

As a result, in a test where the server has a file of size
0x7fffffffffffffff, and the client tries to read from the offset
0x7ffffffffffff000, the read causes loff_t overflow in the server and it
returns an NFS code of EINVAL to the client. The client as a result
indefinitely retries the request.

This fixes the issue at server side by trimming reads past
NFS_OFFSET_MAX. It also adds a missing check for out of bound offset
in NFSv3.

Fixes: 8cfb9015280d ("NFS: Always provide aligned buffers to the RPC read layers")
Signed-off-by: Dan Aloni <dan.aloni@vastdata.com>
---
 fs/nfsd/nfs4proc.c |  3 +++
 fs/nfsd/vfs.c      | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 486c5dba4b65..3b1e395a93b6 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -788,6 +788,9 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	trace_nfsd_read_start(rqstp, &cstate->current_fh,
 			      read->rd_offset, read->rd_length);
 
+	if (unlikely(read->rd_offset + read->rd_length > NFS_OFFSET_MAX))
+		read->rd_length = NFS_OFFSET_MAX - read->rd_offset;
+
 	/*
 	 * If we do a zero copy read, then a client will see read data
 	 * that reflects the state of the file *after* performing the
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 738d564ca4ce..4a209f807466 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1046,6 +1046,16 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	__be32 err;
 
 	trace_nfsd_read_start(rqstp, fhp, offset, *count);
+
+	if (unlikely(offset > NFS_OFFSET_MAX)) {
+		/* We can return this according to Section 3.3.6 */
+		err = nfserr_inval;
+		goto error;
+	}
+
+	if (unlikely(offset + *count > NFS_OFFSET_MAX))
+		*count = NFS_OFFSET_MAX - offset;
+
 	err = nfsd_file_acquire(rqstp, fhp, NFSD_MAY_READ, &nf);
 	if (err)
 		return err;
@@ -1058,6 +1068,7 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	nfsd_file_put(nf);
 
+error:
 	trace_nfsd_read_done(rqstp, fhp, offset, *count);
 
 	return err;
-- 
2.23.0