git.seregonwar.com

src/ftp_buffer_pool.c

zftpd / src / ftp_buffer_pool.c

1	/*
2	MIT License
3
4	Copyright (c) 2026 Seregon
5
6	Permission is hereby granted, free of charge, to any person obtaining a copy
7	of this software and associated documentation files (the "Software"), to deal
8	in the Software without restriction, including without limitation the rights
9	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10	copies of the Software, and to permit persons to whom the Software is
11	furnished to do so, subject to the following conditions:
12
13	The above copyright notice and this permission notice shall be included in all
14	copies or substantial portions of the Software.
15
16	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22	SOFTWARE.
23	*/
24	/**
25	* @file ftp_buffer_pool.h
26	* @brief FTP stream buffer pool
27	*
28	* @author Seregon
29	* @version 1.0.0
30	*
31	* PLATFORMS: FreeBSD (PS4/PS5 kqueue), Linux (epoll)
32	* DESIGN: Single-threaded, non-blocking I/O
33	*
34	*/
35	#include "ftp_buffer_pool.h"
36
37	#include "ftp_config.h"
38	#include <stdatomic.h>
39	#include <stdint.h>
40
41	#ifndef FTP_STREAM_BUFFER_SIZE
42	#define FTP_STREAM_BUFFER_SIZE 65536U
43	#endif
44
45	#ifndef FTP_STREAM_BUFFER_COUNT
46	#define FTP_STREAM_BUFFER_COUNT FTP_MAX_SESSIONS
47	#endif
48
49	static _Alignas(64) uint8_t
50	g_stream_buffers[FTP_STREAM_BUFFER_COUNT][FTP_STREAM_BUFFER_SIZE];
51	static atomic_uint_fast32_t g_stream_buffer_mask = ATOMIC_VAR_INIT(0U);
52
53	/*
54	* VULN-06 fix: guard against 1U << i undefined behavior
55	*
56	* FTP_MAX_SESSIONS up to 256 is allowed by ftp_config.h,
57	* but the bitmask is uint_fast32_t (may be 32-bit on ARM).
58	* If BUFFER_COUNT > bit width, slots beyond bit 31 are
59	* invisible and those sessions can never acquire a buffer.
60	*
61	* This assert fires at compile time if misconfigured.
62	*/
63	_Static_assert(FTP_STREAM_BUFFER_COUNT <= (sizeof(uint_fast32_t) * 8U),
64	"FTP_STREAM_BUFFER_COUNT exceeds atomic bitmask width "
65	"(reduce FTP_MAX_SESSIONS or widen the mask type)");
66
67	void *ftp_buffer_acquire(void) {
68	for (;;) {
69	uint_fast32_t mask = atomic_load(&g_stream_buffer_mask);
70
71	uint_fast32_t found = 0U;
72	for (uint_fast32_t i = 0U; i < (uint_fast32_t)FTP_STREAM_BUFFER_COUNT;
73	i++) {
74	uint_fast32_t bit = 1U << i;
75	if ((mask & bit) != 0U) {
76	continue;
77	}
78
79	uint_fast32_t expected = mask;
80	uint_fast32_t desired = mask \| bit;
81	if (atomic_compare_exchange_strong(&g_stream_buffer_mask, &expected,
82	desired)) {
83	return (void *)g_stream_buffers[i];
84	}
85
86	found = 1U;
87	break; /* CAS failed, re-read mask from outer loop */
88	}
89
90	/*
91	* If CAS failed (found==1), the outer loop retries with a fresh mask.
92	* If no free slot was found (found==0), check if mask changed
93	* since we read it; if unchanged, all buffers are truly occupied.
94	*/
95	if ((found == 0U) && (mask == atomic_load(&g_stream_buffer_mask))) {
96	return NULL;
97	}
98	}
99	}
100
101	void ftp_buffer_release(void *buffer) {
102	if (buffer == NULL) {
103	return;
104	}
105
106	for (uint_fast32_t i = 0U; i < (uint_fast32_t)FTP_STREAM_BUFFER_COUNT; i++) {
107	if ((void *)g_stream_buffers[i] == buffer) {
108	uint_fast32_t bit = 1U << i;
109	(void)atomic_fetch_and(&g_stream_buffer_mask, ~bit);
110	return;
111	}
112	}
113	}
114
115	size_t ftp_buffer_size(void) { return (size_t)FTP_STREAM_BUFFER_SIZE; }
116

Seregon/zftpd