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 inode *inode = folio->mapping->host;
103	struct buffer_head *bh = NULL;
104	unsigned char *symlink;
105	int err = 0;
106	unsigned char *p = folio_address(folio);
107	struct udf_inode_info *iinfo = UDF_I(inode);
108
109	/* We don't support symlinks longer than one block */
110	if (inode->i_size > inode->i_sb->s_blocksize) {
111		err = -ENAMETOOLONG;
112		goto out;
113	}
114
115	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
116		symlink = iinfo->i_data + iinfo->i_lenEAttr;
117	} else {
118		bh = udf_bread(inode, 0, 0, &err);
119		if (!bh) {
120			if (!err)
121				err = -EFSCORRUPTED;
122			goto out;
123		}
124		symlink = bh->b_data;
125	}
126
127	err = udf_pc_to_char(inode->i_sb, symlink, inode->i_size, p, PAGE_SIZE);
128	brelse(bh);
129out:
130	folio_end_read(folio, err == 0);
131	return err;
132}
133
134static int udf_symlink_getattr(struct mnt_idmap *idmap,
135			       const struct path *path, struct kstat *stat,
136			       u32 request_mask, unsigned int flags)
137{
138	struct dentry *dentry = path->dentry;
139	struct inode *inode = d_backing_inode(dentry);
140	struct folio *folio;
141
142	generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
143	folio = read_mapping_folio(inode->i_mapping, 0, NULL);
144	if (IS_ERR(folio))
145		return PTR_ERR(folio);
146	/*
147	 * UDF uses non-trivial encoding of symlinks so i_size does not match
148	 * number of characters reported by readlink(2) which apparently some
149	 * applications expect. Also POSIX says that "The value returned in the
150	 * st_size field shall be the length of the contents of the symbolic
151	 * link, and shall not count a trailing null if one is present." So
152	 * let's report the length of string returned by readlink(2) for
153	 * st_size.
154	 */
155	stat->size = strlen(folio_address(folio));
156	folio_put(folio);
157
158	return 0;
159}
160
161/*
162 * symlinks can't do much...
163 */
164const struct address_space_operations udf_symlink_aops = {
165	.read_folio		= udf_symlink_filler,
166};
167
168const struct inode_operations udf_symlink_inode_operations = {
169	.get_link	= page_get_link,
170	.getattr	= udf_symlink_getattr,
171};
172