lockd: set file_lock start and end when decoding nlm4 testargs

Commit 6930bcbfb6ce dropped the setting of the file_lock range when
decoding a nlm_lock off the wire. This causes the client side grant
callback to miss matching blocks and reject the lock, only to rerequest
it 30s later.

Add a helper function to set the file_lock range from the start and end
values that the protocol uses, and have the nlm_lock decoder call that to
set up the file_lock args properly.

Fixes: 6930bcbfb6ce ("lockd: detect and reject lock arguments that overflow")
Reported-by: Amir Goldstein <[e-mail]>
Signed-off-by: Jeff Layton <[e-mail]>
Tested-by: Amir Goldstein <[e-mail]>
Cc: [e-mail] #6.0
Signed-off-by: Anna Schumaker <[e-mail]>

fs/lockd/clnt4xdr.c

···
 	u32 exclusive;
 	int error;
 	__be32 *p;
-	s32 end;
 
 	memset(lock, 0, sizeof(*lock));
 	locks_init_lock(fl);
···
 	fl->fl_type  = exclusive != 0 ? F_WRLCK : F_RDLCK;
 	p = xdr_decode_hyper(p, &l_offset);
 	xdr_decode_hyper(p, &l_len);
-	end = l_offset + l_len - 1;
-
-	fl->fl_start = (loff_t)l_offset;
-	if (l_len == 0 || end < 0)
-		fl->fl_end = OFFSET_MAX;
-	else
-		fl->fl_end = (loff_t)end;
+	nlm4svc_set_file_lock_range(fl, l_offset, l_len);
 	error = 0;
 out:
 	return error;

fs/lockd/xdr4.c

···
 	return res;
 }
 
+void nlm4svc_set_file_lock_range(struct file_lock *fl, u64 off, u64 len)
+{
+	s64 end = off + len - 1;
+
+	fl->fl_start = off;
+	if (len == 0 || end < 0)
+		fl->fl_end = OFFSET_MAX;
+	else
+		fl->fl_end = end;
+}
+
 /*
  * NLM file handles are defined by specification to be a variable-length
  * XDR opaque no longer than 1024 bytes. However, this implementation
···
 	locks_init_lock(fl);
 	fl->fl_flags = FL_POSIX;
 	fl->fl_type  = F_RDLCK;
-
+	nlm4svc_set_file_lock_range(fl, lock->lock_start, lock->lock_len);
 	return true;
 }
 

include/linux/lockd/xdr4.h

···
 #define	nlm4_fbig		cpu_to_be32(NLM_FBIG)
 #define	nlm4_failed		cpu_to_be32(NLM_FAILED)
 
+void	nlm4svc_set_file_lock_range(struct file_lock *fl, u64 off, u64 len);
 bool	nlm4svc_decode_void(struct svc_rqst *rqstp, struct xdr_stream *xdr);
 bool	nlm4svc_decode_testargs(struct svc_rqst *rqstp, struct xdr_stream *xdr);
 bool	nlm4svc_decode_lockargs(struct svc_rqst *rqstp, struct xdr_stream *xdr);