[PATCH v3] NFSD: trim reads past NFS_OFFSET_MAX and fix NFSv3 check

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

Due to commit 8cfb9015280d ("NFS: Always provide aligned buffers to the
RPC read layers") on the client, a read of 0xfff is aligned up to server
rsize of 0x1000.

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, copying a similar check from NFSv4.x.

Cc: <stable@vger.kernel.org>
Signed-off-by: Dan Aloni <dan.aloni@vastdata.com>
---
 fs/nfsd/nfs4proc.c | 3 +++
 fs/nfsd/vfs.c      | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 486c5dba4b65..816bdf212559 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -785,6 +785,9 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	if (read->rd_offset >= OFFSET_MAX)
 		return nfserr_inval;
 
+	if (unlikely(read->rd_offset + read->rd_length > OFFSET_MAX))
+		read->rd_length = OFFSET_MAX - read->rd_offset;
+
 	trace_nfsd_read_start(rqstp, &cstate->current_fh,
 			      read->rd_offset, read->rd_length);
 
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 738d564ca4ce..ad4df374433e 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1045,6 +1045,12 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	struct file *file;
 	__be32 err;
 
+	if (unlikely(offset >= NFS_OFFSET_MAX))
+		return nfserr_inval;
+
+	if (unlikely(offset + *count > NFS_OFFSET_MAX))
+		*count = NFS_OFFSET_MAX - offset;
+
 	trace_nfsd_read_start(rqstp, fhp, offset, *count);
 	err = nfsd_file_acquire(rqstp, fhp, NFSD_MAY_READ, &nf);
 	if (err)
-- 
2.23.0