fs/udf/symlink.c

   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
  28 static 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
 100 static 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);
 129 out:
 130         folio_end_read(folio, err == 0);
 131         return err;
 132 }
 133
 134 static 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  */
 164 const struct address_space_operations udf_symlink_aops = {
 165         .read_folio             = udf_symlink_filler,
 166 };
 167
 168 const struct inode_operations udf_symlink_inode_operations = {
 169         .get_link       = page_get_link,
 170         .getattr        = udf_symlink_getattr,
 171 };