fs/udf/symlink.c

   1 /*
   2  * symlink.c
   3  *
   4  * PURPOSE
   5  *      Symlink handling routines for the OSTA-UDF(tm) filesystem.
   6  *
   7  * COPYRIGHT
   8  *      This file is distributed under the terms of the GNU General Public
   9  *      License (GPL). Copies of the GPL can be obtained from:
  10  *              ftp://prep.ai.mit.edu/pub/gnu/GPL
  11  *      Each contributing author retains all rights to their own work.
  12  *
  13  *  (C) 1998-2001 Ben Fennema
  14  *  (C) 1999 Stelias Computing Inc
  15  *
  16  * HISTORY
  17  *
  18  *  04/16/99 blf  Created.
  19  *
  20  */
  21
  22 #include "udfdecl.h"
  23 #include <linux/uaccess.h>
  24 #include <linux/errno.h>
  25 #include <linux/fs.h>
  26 #include <linux/time.h>
  27 #include <linux/mm.h>
  28 #include <linux/stat.h>
  29 #include <linux/pagemap.h>
  30 #include "udf_i.h"
  31
  32 static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
  33                           int fromlen, unsigned char *to, int tolen)
  34 {
  35         struct pathComponent *pc;
  36         int elen = 0;
  37         int comp_len;
  38         unsigned char *p = to;
  39
  40         /* Reserve one byte for terminating \0 */
  41         tolen--;
  42         while (elen < fromlen) {
  43                 pc = (struct pathComponent *)(from + elen);
  44                 elen += sizeof(struct pathComponent);
  45                 switch (pc->componentType) {
  46                 case 1:
  47                         /*
  48                          * Symlink points to some place which should be agreed
  49                          * upon between originator and receiver of the media. Ignore.
  50                          */
  51                         if (pc->lengthComponentIdent > 0) {
  52                                 elen += pc->lengthComponentIdent;
  53                                 break;
  54                         }
  55                         fallthrough;
  56                 case 2:
  57                         if (tolen == 0)
  58                                 return -ENAMETOOLONG;
  59                         p = to;
  60                         *p++ = '/';
  61                         tolen--;
  62                         break;
  63                 case 3:
  64                         if (tolen < 3)
  65                                 return -ENAMETOOLONG;
  66                         memcpy(p, "../", 3);
  67                         p += 3;
  68                         tolen -= 3;
  69                         break;
  70                 case 4:
  71                         if (tolen < 2)
  72                                 return -ENAMETOOLONG;
  73                         memcpy(p, "./", 2);
  74                         p += 2;
  75                         tolen -= 2;
  76                         /* that would be . - just ignore */
  77                         break;
  78                 case 5:
  79                         elen += pc->lengthComponentIdent;
  80                         if (elen > fromlen)
  81                                 return -EIO;
  82                         comp_len = udf_get_filename(sb, pc->componentIdent,
  83                                                     pc->lengthComponentIdent,
  84                                                     p, tolen);
  85                         if (comp_len < 0)
  86                                 return comp_len;
  87
  88                         p += comp_len;
  89                         tolen -= comp_len;
  90                         if (tolen == 0)
  91                                 return -ENAMETOOLONG;
  92                         *p++ = '/';
  93                         tolen--;
  94                         break;
  95                 }
  96         }
  97         if (p > to + 1)
  98                 p[-1] = '\0';
  99         else
 100                 p[0] = '\0';
 101         return 0;
 102 }
 103
 104 static int udf_symlink_filler(struct file *file, struct page *page)
 105 {
 106         struct inode *inode = page->mapping->host;
 107         struct buffer_head *bh = NULL;
 108         unsigned char *symlink;
 109         int err;
 110         unsigned char *p = page_address(page);
 111         struct udf_inode_info *iinfo;
 112         uint32_t pos;
 113
 114         /* We don't support symlinks longer than one block */
 115         if (inode->i_size > inode->i_sb->s_blocksize) {
 116                 err = -ENAMETOOLONG;
 117                 goto out_unmap;
 118         }
 119
 120         iinfo = UDF_I(inode);
 121         pos = udf_block_map(inode, 0);
 122
 123         down_read(&iinfo->i_data_sem);
 124         if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
 125                 symlink = iinfo->i_data + iinfo->i_lenEAttr;
 126         } else {
 127                 bh = sb_bread(inode->i_sb, pos);
 128
 129                 if (!bh) {
 130                         err = -EIO;
 131                         goto out_unlock_inode;
 132                 }
 133
 134                 symlink = bh->b_data;
 135         }
 136
 137         err = udf_pc_to_char(inode->i_sb, symlink, inode->i_size, p, PAGE_SIZE);
 138         brelse(bh);
 139         if (err)
 140                 goto out_unlock_inode;
 141
 142         up_read(&iinfo->i_data_sem);
 143         SetPageUptodate(page);
 144         unlock_page(page);
 145         return 0;
 146
 147 out_unlock_inode:
 148         up_read(&iinfo->i_data_sem);
 149         SetPageError(page);
 150 out_unmap:
 151         unlock_page(page);
 152         return err;
 153 }
 154
 155 static int udf_symlink_getattr(struct user_namespace *mnt_userns,
 156                                const struct path *path, struct kstat *stat,
 157                                u32 request_mask, unsigned int flags)
 158 {
 159         struct dentry *dentry = path->dentry;
 160         struct inode *inode = d_backing_inode(dentry);
 161         struct page *page;
 162
 163         generic_fillattr(&init_user_ns, inode, stat);
 164         page = read_mapping_page(inode->i_mapping, 0, NULL);
 165         if (IS_ERR(page))
 166                 return PTR_ERR(page);
 167         /*
 168          * UDF uses non-trivial encoding of symlinks so i_size does not match
 169          * number of characters reported by readlink(2) which apparently some
 170          * applications expect. Also POSIX says that "The value returned in the
 171          * st_size field shall be the length of the contents of the symbolic
 172          * link, and shall not count a trailing null if one is present." So
 173          * let's report the length of string returned by readlink(2) for
 174          * st_size.
 175          */
 176         stat->size = strlen(page_address(page));
 177         put_page(page);
 178
 179         return 0;
 180 }
 181
 182 /*
 183  * symlinks can't do much...
 184  */
 185 const struct address_space_operations udf_symlink_aops = {
 186         .readpage               = udf_symlink_filler,
 187 };
 188
 189 const struct inode_operations udf_symlink_inode_operations = {
 190         .get_link       = page_get_link,
 191         .getattr        = udf_symlink_getattr,
 192 };