1 /***************************************************************************
2 * Copyright (c) 2024 Microsoft Corporation
3 *
4 * This program and the accompanying materials are made available under the
5 * terms of the MIT License which is available at
6 * https://opensource.org/licenses/MIT.
7 *
8 * SPDX-License-Identifier: MIT
9 **************************************************************************/
10
11
12 /**************************************************************************/
13 /**************************************************************************/
14 /** */
15 /** NetX Component */
16 /** */
17 /** Transmission Control Protocol (TCP) */
18 /** */
19 /**************************************************************************/
20 /**************************************************************************/
21
22 #define NX_SOURCE_CODE
23
24
25 /* Include necessary system files. */
26
27 #include "nx_api.h"
28 #include "nx_tcp.h"
29
30
31 /**************************************************************************/
32 /* */
33 /* FUNCTION RELEASE */
34 /* */
35 /* _nx_tcp_mss_option_get PORTABLE C */
36 /* 6.1 */
37 /* AUTHOR */
38 /* */
39 /* Yuxin Zhou, Microsoft Corporation */
40 /* */
41 /* DESCRIPTION */
42 /* */
43 /* This function searches for the Maximum Segment Size (MSS) option. */
44 /* If found, first check the option length, if option length is not */
45 /* valid, it returns NX_FALSE to the caller, else it set the mss value */
46 /* and returns NX_TRUE to the caller. Otherwise, NX_TRUE is returned. */
47 /* */
48 /* INPUT */
49 /* */
50 /* option_ptr Pointer to option area */
51 /* option_area_size Size of option area */
52 /* mss Max segment size */
53 /* */
54 /* OUTPUT */
55 /* */
56 /* NX_FALSE TCP option is invalid */
57 /* NX_TRUE TCP option is valid */
58 /* */
59 /* CALLS */
60 /* */
61 /* None */
62 /* */
63 /* CALLED BY */
64 /* */
65 /* _nx_tcp_packet_process TCP packet processing */
66 /* _nx_tcp_server_socket_relisten Socket relisten processing */
67 /* */
68 /* RELEASE HISTORY */
69 /* */
70 /* DATE NAME DESCRIPTION */
71 /* */
72 /* 05-19-2020 Yuxin Zhou Initial Version 6.0 */
73 /* 09-30-2020 Yuxin Zhou Modified comment(s), */
74 /* resulting in version 6.1 */
75 /* */
76 /**************************************************************************/
_nx_tcp_mss_option_get(UCHAR * option_ptr,ULONG option_area_size,ULONG * mss)77 UINT _nx_tcp_mss_option_get(UCHAR *option_ptr, ULONG option_area_size, ULONG *mss)
78 {
79
80 ULONG option_length;
81
82 /* Initialize the value. */
83 *mss = 0;
84
85 /* Loop through the option area looking for the MSS. */
86 while (option_area_size >= 4)
87 {
88
89 /* Is the current character the MSS type? */
90 if (*option_ptr == NX_TCP_MSS_KIND)
91 {
92
93 /* Yes, we found it! */
94
95 /* Move the pointer forward by one. */
96 option_ptr++;
97
98 /* Check the option length, if option length is not equal to 4, return NX_FALSE. */
99 if (*option_ptr++ != 4)
100 {
101 return(NX_FALSE);
102 }
103
104 /* Build the mss size. */
105 *mss = (ULONG)*option_ptr++;
106
107 /* Get the LSB of the MSS. */
108 *mss = (*mss << 8) | (ULONG)*option_ptr;
109
110 /* Finished, get out of the loop! */
111 break;
112 }
113
114 /* Otherwise, process relative to the option type. */
115
116 /* Check for end of list. */
117 if (*option_ptr == NX_TCP_EOL_KIND)
118 {
119
120 /* Yes, end of list, get out! */
121 break;
122 }
123
124 /* Check for NOP. */
125 if (*option_ptr++ == NX_TCP_NOP_KIND)
126 {
127
128 /* One character option! */
129 option_area_size--;
130 }
131 else
132 {
133
134 /* Derive the option length. */
135 option_length = ((ULONG)*option_ptr);
136
137 /* Return when option length is invalid. */
138 if (option_length == 0)
139 {
140 return(NX_FALSE);
141 }
142
143 /* Move the option pointer forward. */
144 option_ptr = option_ptr + (option_length - 1);
145
146 /* Determine if this is greater than the option area size. */
147 if (option_length > option_area_size)
148 {
149 return(NX_FALSE);
150 }
151 else
152 {
153 option_area_size = option_area_size - option_length;
154 }
155 }
156 }
157
158 /* Return. */
159 return(NX_TRUE);
160 }
161
162
