1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * symlink.c
4 *
5 * PURPOSE
6 *	Symlink handling routines for the OSTA-UDF(tm) filesystem.
7 *
8 * COPYRIGHT
9 *  (C) 1998-2001 Ben Fennema
10 *  (C) 1999 Stelias Computing Inc
11 *
12 * HISTORY
13 *
14 *  04/16/99 blf  Created.
15 *
16 */
17
18#include "udfdecl.h"
19#include <linux/uaccess.h>
20#include <linux/errno.h>
21#include <linux/fs.h>
22#include <linux/time.h>
23#include <linux/mm.h>
24#include <linux/stat.h>
25#include <linux/pagemap.h>
26#include "udf_i.h"
27
28static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
29			  int fromlen, unsigned char *to, int tolen)
30{
31	struct pathComponent *pc;
32	int elen = 0;
33	int comp_len;
34	unsigned char *p = to;
35
36	/* Reserve one byte for terminating \0 */
37	tolen--;
38	while (elen < fromlen) {
39		pc = (struct pathComponent *)(from + elen);
40		elen += sizeof(struct pathComponent);
41		switch (pc->componentType) {
42		case 1:
43			/*
44			 * Symlink points to some place which should be agreed
45 			 * upon between originator and receiver of the media. Ignore.
46			 */
47			if (pc->lengthComponentIdent > 0) {
48				elen += pc->lengthComponentIdent;
49				break;
50			}
51			fallthrough;
52		case 2:
53			if (tolen == 0)
54				return -ENAMETOOLONG;
55			p = to;
56			*p++ = '/';
57			tolen--;
58			break;
59		case 3:
60			if (tolen < 3)
61				return -ENAMETOOLONG;
62			memcpy(p, "../", 3);
63			p += 3;
64			tolen -= 3;
65			break;
66		case 4:
67			if (tolen < 2)
68				return -ENAMETOOLONG;
69			memcpy(p, "./", 2);
70			p += 2;
71			tolen -= 2;
72			/* that would be . - just ignore */
73			break;
74		case 5:
75			elen += pc->lengthComponentIdent;
76			if (elen > fromlen)
77				return -EIO;
78			comp_len = udf_get_filename(sb, pc->componentIdent,
79						    pc->lengthComponentIdent,
80						    p, tolen);
81			if (comp_len < 0)
82				return comp_len;
83
84			p += comp_len;
85			tolen -= comp_len;
86			if (tolen == 0)
87				return -ENAMETOOLONG;
88			*p++ = '/';
89			tolen--;
90			break;
91		}
92	}
93	if (p > to + 1)
94		p[-1] = '\0';
95	else
96		p[0] = '\0';
97	return 0;
98}
99
100static int udf_symlink_filler(struct file *file, struct folio *folio)
101{
102	struct page *page = &folio->page;
103	struct inode *inode = page->mapping->host;
104	struct buffer_head *bh = NULL;
105	unsigned char *symlink;
106	int err = 0;
107	unsigned char *p = page_address(page);
108	struct udf_inode_info *iinfo = UDF_I(inode);
109
110	/* We don't support symlinks longer than one block */
111	if (inode->i_size > inode->i_sb->s_blocksize) {
112		err = -ENAMETOOLONG;
113		goto out_unlock;
114	}
115
116	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
117		symlink = iinfo->i_data + iinfo->i_lenEAttr;
118	} else {
119		bh = udf_bread(inode, 0, 0, &err);
120		if (!bh) {
121			if (!err)
122				err = -EFSCORRUPTED;
123			goto out_err;
124		}
125		symlink = bh->b_data;
126	}
127
128	err = udf_pc_to_char(inode->i_sb, symlink, inode->i_size, p, PAGE_SIZE);
129	brelse(bh);
130	if (err)
131		goto out_err;
132
133	SetPageUptodate(page);
134	unlock_page(page);
135	return 0;
136
137out_err:
138	SetPageError(page);
139out_unlock:
140	unlock_page(page);
141	return err;
142}
143
144static int udf_symlink_getattr(struct mnt_idmap *idmap,
145			       const struct path *path, struct kstat *stat,
146			       u32 request_mask, unsigned int flags)
147{
148	struct dentry *dentry = path->dentry;
149	struct inode *inode = d_backing_inode(dentry);
150	struct page *page;
151
152	generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
153	page = read_mapping_page(inode->i_mapping, 0, NULL);
154	if (IS_ERR(page))
155		return PTR_ERR(page);
156	/*
157	 * UDF uses non-trivial encoding of symlinks so i_size does not match
158	 * number of characters reported by readlink(2) which apparently some
159	 * applications expect. Also POSIX says that "The value returned in the
160	 * st_size field shall be the length of the contents of the symbolic
161	 * link, and shall not count a trailing null if one is present." So
162	 * let's report the length of string returned by readlink(2) for
163	 * st_size.
164	 */
165	stat->size = strlen(page_address(page));
166	put_page(page);
167
168	return 0;
169}
170
171/*
172 * symlinks can't do much...
173 */
174const struct address_space_operations udf_symlink_aops = {
175	.read_folio		= udf_symlink_filler,
176};
177
178const struct inode_operations udf_symlink_inode_operations = {
179	.get_link	= page_get_link,
180	.getattr	= udf_symlink_getattr,
181};
182