symlink.c 3.3 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153
  1. // SPDX-License-Identifier: GPL-2.0-only
  2. /*
  3. * fs/kernfs/symlink.c - kernfs symlink implementation
  4. *
  5. * Copyright (c) 2001-3 Patrick Mochel
  6. * Copyright (c) 2007 SUSE Linux Products GmbH
  7. * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  8. */
  9. #include <linux/fs.h>
  10. #include <linux/gfp.h>
  11. #include <linux/namei.h>
  12. #include "kernfs-internal.h"
  13. /**
  14. * kernfs_create_link - create a symlink
  15. * @parent: directory to create the symlink in
  16. * @name: name of the symlink
  17. * @target: target node for the symlink to point to
  18. *
  19. * Returns the created node on success, ERR_PTR() value on error.
  20. * Ownership of the link matches ownership of the target.
  21. */
  22. struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
  23. const char *name,
  24. struct kernfs_node *target)
  25. {
  26. struct kernfs_node *kn;
  27. int error;
  28. kuid_t uid = GLOBAL_ROOT_UID;
  29. kgid_t gid = GLOBAL_ROOT_GID;
  30. if (target->iattr) {
  31. uid = target->iattr->ia_uid;
  32. gid = target->iattr->ia_gid;
  33. }
  34. kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, uid, gid,
  35. KERNFS_LINK);
  36. if (!kn)
  37. return ERR_PTR(-ENOMEM);
  38. if (kernfs_ns_enabled(parent))
  39. kn->ns = target->ns;
  40. kn->symlink.target_kn = target;
  41. kernfs_get(target); /* ref owned by symlink */
  42. error = kernfs_add_one(kn);
  43. if (!error)
  44. return kn;
  45. kernfs_put(kn);
  46. return ERR_PTR(error);
  47. }
  48. static int kernfs_get_target_path(struct kernfs_node *parent,
  49. struct kernfs_node *target, char *path)
  50. {
  51. struct kernfs_node *base, *kn;
  52. char *s = path;
  53. int len = 0;
  54. /* go up to the root, stop at the base */
  55. base = parent;
  56. while (base->parent) {
  57. kn = target->parent;
  58. while (kn->parent && base != kn)
  59. kn = kn->parent;
  60. if (base == kn)
  61. break;
  62. if ((s - path) + 3 >= PATH_MAX)
  63. return -ENAMETOOLONG;
  64. strcpy(s, "../");
  65. s += 3;
  66. base = base->parent;
  67. }
  68. /* determine end of target string for reverse fillup */
  69. kn = target;
  70. while (kn->parent && kn != base) {
  71. len += strlen(kn->name) + 1;
  72. kn = kn->parent;
  73. }
  74. /* check limits */
  75. if (len < 2)
  76. return -EINVAL;
  77. len--;
  78. if ((s - path) + len >= PATH_MAX)
  79. return -ENAMETOOLONG;
  80. /* reverse fillup of target string from target to base */
  81. kn = target;
  82. while (kn->parent && kn != base) {
  83. int slen = strlen(kn->name);
  84. len -= slen;
  85. memcpy(s + len, kn->name, slen);
  86. if (len)
  87. s[--len] = '/';
  88. kn = kn->parent;
  89. }
  90. return 0;
  91. }
  92. static int kernfs_getlink(struct inode *inode, char *path)
  93. {
  94. struct kernfs_node *kn = inode->i_private;
  95. struct kernfs_node *parent = kn->parent;
  96. struct kernfs_node *target = kn->symlink.target_kn;
  97. int error;
  98. mutex_lock(&kernfs_mutex);
  99. error = kernfs_get_target_path(parent, target, path);
  100. mutex_unlock(&kernfs_mutex);
  101. return error;
  102. }
  103. static const char *kernfs_iop_get_link(struct dentry *dentry,
  104. struct inode *inode,
  105. struct delayed_call *done)
  106. {
  107. char *body;
  108. int error;
  109. if (!dentry)
  110. return ERR_PTR(-ECHILD);
  111. body = kzalloc(PAGE_SIZE, GFP_KERNEL);
  112. if (!body)
  113. return ERR_PTR(-ENOMEM);
  114. error = kernfs_getlink(inode, body);
  115. if (unlikely(error < 0)) {
  116. kfree(body);
  117. return ERR_PTR(error);
  118. }
  119. set_delayed_call(done, kfree_link, body);
  120. return body;
  121. }
  122. const struct inode_operations kernfs_symlink_iops = {
  123. .listxattr = kernfs_iop_listxattr,
  124. .get_link = kernfs_iop_get_link,
  125. .setattr = kernfs_iop_setattr,
  126. .getattr = kernfs_iop_getattr,
  127. .permission = kernfs_iop_permission,
  128. };