[PATCH] NFSD: trim reads past NFS_OFFSET_MAX

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

Due to change 8cfb9015280d ("NFS: Always provide aligned buffers to the
RPC read layers"), 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.

Fixes: 8cfb9015280d ("NFS: Always provide aligned buffers to the RPC read layers")
Signed-off-by: Dan Aloni <dan.aloni@vastdata.com>
---
 fs/nfsd/vfs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 738d564ca4ce..754f4e9ff4a2 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1046,6 +1046,10 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	__be32 err;
 
 	trace_nfsd_read_start(rqstp, fhp, offset, *count);
+
+	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;
-- 
2.23.0