fs/attr.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/attr.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  *  changes by Thomas Schoebel-Theuer
   7  */
   8
   9 #include <linux/export.h>
  10 #include <linux/time.h>
  11 #include <linux/mm.h>
  12 #include <linux/string.h>
  13 #include <linux/sched/signal.h>
  14 #include <linux/capability.h>
  15 #include <linux/fsnotify.h>
  16 #include <linux/fcntl.h>
  17 #include <linux/security.h>
  18 #include <linux/evm.h>
  19 #include <linux/ima.h>
  20
  21 static bool chown_ok(const struct inode *inode, kuid_t uid)
  22 {
  23         if (uid_eq(current_fsuid(), inode->i_uid) &&
  24             uid_eq(uid, inode->i_uid))
  25                 return true;
  26         if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  27                 return true;
  28         if (uid_eq(inode->i_uid, INVALID_UID) &&
  29             ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  30                 return true;
  31         return false;
  32 }
  33
  34 static bool chgrp_ok(const struct inode *inode, kgid_t gid)
  35 {
  36         if (uid_eq(current_fsuid(), inode->i_uid) &&
  37             (in_group_p(gid) || gid_eq(gid, inode->i_gid)))
  38                 return true;
  39         if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  40                 return true;
  41         if (gid_eq(inode->i_gid, INVALID_GID) &&
  42             ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  43                 return true;
  44         return false;
  45 }
  46
  47 /**
  48  * setattr_prepare - check if attribute changes to a dentry are allowed
  49  * @dentry:     dentry to check
  50  * @attr:       attributes to change
  51  *
  52  * Check if we are allowed to change the attributes contained in @attr
  53  * in the given dentry.  This includes the normal unix access permission
  54  * checks, as well as checks for rlimits and others. The function also clears
  55  * SGID bit from mode if user is not allowed to set it. Also file capabilities
  56  * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
  57  *
  58  * Should be called as the first thing in ->setattr implementations,
  59  * possibly after taking additional locks.
  60  */
  61 int setattr_prepare(struct dentry *dentry, struct iattr *attr)
  62 {
  63         struct inode *inode = d_inode(dentry);
  64         unsigned int ia_valid = attr->ia_valid;
  65
  66         /*
  67          * First check size constraints.  These can't be overriden using
  68          * ATTR_FORCE.
  69          */
  70         if (ia_valid & ATTR_SIZE) {
  71                 int error = inode_newsize_ok(inode, attr->ia_size);
  72                 if (error)
  73                         return error;
  74         }
  75
  76         /* If force is set do it anyway. */
  77         if (ia_valid & ATTR_FORCE)
  78                 goto kill_priv;
  79
  80         /* Make sure a caller can chown. */
  81         if ((ia_valid & ATTR_UID) && !chown_ok(inode, attr->ia_uid))
  82                 return -EPERM;
  83
  84         /* Make sure caller can chgrp. */
  85         if ((ia_valid & ATTR_GID) && !chgrp_ok(inode, attr->ia_gid))
  86                 return -EPERM;
  87
  88         /* Make sure a caller can chmod. */
  89         if (ia_valid & ATTR_MODE) {
  90                 if (!inode_owner_or_capable(inode))
  91                         return -EPERM;
  92                 /* Also check the setgid bit! */
  93                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  94                                 inode->i_gid) &&
  95                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
  96                         attr->ia_mode &= ~S_ISGID;
  97         }
  98
  99         /* Check for setting the inode time. */
 100         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
 101                 if (!inode_owner_or_capable(inode))
 102                         return -EPERM;
 103         }
 104
 105 kill_priv:
 106         /* User has permission for the change */
 107         if (ia_valid & ATTR_KILL_PRIV) {
 108                 int error;
 109
 110                 error = security_inode_killpriv(dentry);
 111                 if (error)
 112                         return error;
 113         }
 114
 115         return 0;
 116 }
 117 EXPORT_SYMBOL(setattr_prepare);
 118
 119 /**
 120  * inode_newsize_ok - may this inode be truncated to a given size
 121  * @inode:      the inode to be truncated
 122  * @offset:     the new size to assign to the inode
 123  *
 124  * inode_newsize_ok must be called with i_mutex held.
 125  *
 126  * inode_newsize_ok will check filesystem limits and ulimits to check that the
 127  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
 128  * when necessary. Caller must not proceed with inode size change if failure is
 129  * returned. @inode must be a file (not directory), with appropriate
 130  * permissions to allow truncate (inode_newsize_ok does NOT check these
 131  * conditions).
 132  *
 133  * Return: 0 on success, -ve errno on failure
 134  */
 135 int inode_newsize_ok(const struct inode *inode, loff_t offset)
 136 {
 137         if (inode->i_size < offset) {
 138                 unsigned long limit;
 139
 140                 limit = rlimit(RLIMIT_FSIZE);
 141                 if (limit != RLIM_INFINITY && offset > limit)
 142                         goto out_sig;
 143                 if (offset > inode->i_sb->s_maxbytes)
 144                         goto out_big;
 145         } else {
 146                 /*
 147                  * truncation of in-use swapfiles is disallowed - it would
 148                  * cause subsequent swapout to scribble on the now-freed
 149                  * blocks.
 150                  */
 151                 if (IS_SWAPFILE(inode))
 152                         return -ETXTBSY;
 153         }
 154
 155         return 0;
 156 out_sig:
 157         send_sig(SIGXFSZ, current, 0);
 158 out_big:
 159         return -EFBIG;
 160 }
 161 EXPORT_SYMBOL(inode_newsize_ok);
 162
 163 /**
 164  * setattr_copy - copy simple metadata updates into the generic inode
 165  * @inode:      the inode to be updated
 166  * @attr:       the new attributes
 167  *
 168  * setattr_copy must be called with i_mutex held.
 169  *
 170  * setattr_copy updates the inode's metadata with that specified
 171  * in attr. Noticeably missing is inode size update, which is more complex
 172  * as it requires pagecache updates.
 173  *
 174  * The inode is not marked as dirty after this operation. The rationale is
 175  * that for "simple" filesystems, the struct inode is the inode storage.
 176  * The caller is free to mark the inode dirty afterwards if needed.
 177  */
 178 void setattr_copy(struct inode *inode, const struct iattr *attr)
 179 {
 180         unsigned int ia_valid = attr->ia_valid;
 181
 182         if (ia_valid & ATTR_UID)
 183                 inode->i_uid = attr->ia_uid;
 184         if (ia_valid & ATTR_GID)
 185                 inode->i_gid = attr->ia_gid;
 186         if (ia_valid & ATTR_ATIME)
 187                 inode->i_atime = attr->ia_atime;
 188         if (ia_valid & ATTR_MTIME)
 189                 inode->i_mtime = attr->ia_mtime;
 190         if (ia_valid & ATTR_CTIME)
 191                 inode->i_ctime = attr->ia_ctime;
 192         if (ia_valid & ATTR_MODE) {
 193                 umode_t mode = attr->ia_mode;
 194
 195                 if (!in_group_p(inode->i_gid) &&
 196                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
 197                         mode &= ~S_ISGID;
 198                 inode->i_mode = mode;
 199         }
 200 }
 201 EXPORT_SYMBOL(setattr_copy);
 202
 203 /**
 204  * notify_change - modify attributes of a filesytem object
 205  * @dentry:     object affected
 206  * @attr:       new attributes
 207  * @delegated_inode: returns inode, if the inode is delegated
 208  *
 209  * The caller must hold the i_mutex on the affected object.
 210  *
 211  * If notify_change discovers a delegation in need of breaking,
 212  * it will return -EWOULDBLOCK and return a reference to the inode in
 213  * delegated_inode.  The caller should then break the delegation and
 214  * retry.  Because breaking a delegation may take a long time, the
 215  * caller should drop the i_mutex before doing so.
 216  *
 217  * Alternatively, a caller may pass NULL for delegated_inode.  This may
 218  * be appropriate for callers that expect the underlying filesystem not
 219  * to be NFS exported.  Also, passing NULL is fine for callers holding
 220  * the file open for write, as there can be no conflicting delegation in
 221  * that case.
 222  */
 223 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
 224 {
 225         struct inode *inode = dentry->d_inode;
 226         umode_t mode = inode->i_mode;
 227         int error;
 228         struct timespec64 now;
 229         unsigned int ia_valid = attr->ia_valid;
 230
 231         WARN_ON_ONCE(!inode_is_locked(inode));
 232
 233         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 234                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 235                         return -EPERM;
 236         }
 237
 238         /*
 239          * If utimes(2) and friends are called with times == NULL (or both
 240          * times are UTIME_NOW), then we need to check for write permission
 241          */
 242         if (ia_valid & ATTR_TOUCH) {
 243                 if (IS_IMMUTABLE(inode))
 244                         return -EPERM;
 245
 246                 if (!inode_owner_or_capable(inode)) {
 247                         error = inode_permission(inode, MAY_WRITE);
 248                         if (error)
 249                                 return error;
 250                 }
 251         }
 252
 253         if ((ia_valid & ATTR_MODE)) {
 254                 umode_t amode = attr->ia_mode;
 255                 /* Flag setting protected by i_mutex */
 256                 if (is_sxid(amode))
 257                         inode->i_flags &= ~S_NOSEC;
 258         }
 259
 260         now = current_time(inode);
 261
 262         attr->ia_ctime = now;
 263         if (!(ia_valid & ATTR_ATIME_SET))
 264                 attr->ia_atime = now;
 265         else
 266                 attr->ia_atime = timestamp_truncate(attr->ia_atime, inode);
 267         if (!(ia_valid & ATTR_MTIME_SET))
 268                 attr->ia_mtime = now;
 269         else
 270                 attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
 271
 272         if (ia_valid & ATTR_KILL_PRIV) {
 273                 error = security_inode_need_killpriv(dentry);
 274                 if (error < 0)
 275                         return error;
 276                 if (error == 0)
 277                         ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
 278         }
 279
 280         /*
 281          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 282          * that the function has the ability to reinterpret a mode change
 283          * that's due to these bits. This adds an implicit restriction that
 284          * no function will ever call notify_change with both ATTR_MODE and
 285          * ATTR_KILL_S*ID set.
 286          */
 287         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 288             (ia_valid & ATTR_MODE))
 289                 BUG();
 290
 291         if (ia_valid & ATTR_KILL_SUID) {
 292                 if (mode & S_ISUID) {
 293                         ia_valid = attr->ia_valid |= ATTR_MODE;
 294                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 295                 }
 296         }
 297         if (ia_valid & ATTR_KILL_SGID) {
 298                 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 299                         if (!(ia_valid & ATTR_MODE)) {
 300                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 301                                 attr->ia_mode = inode->i_mode;
 302                         }
 303                         attr->ia_mode &= ~S_ISGID;
 304                 }
 305         }
 306         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 307                 return 0;
 308
 309         /*
 310          * Verify that uid/gid changes are valid in the target
 311          * namespace of the superblock.
 312          */
 313         if (ia_valid & ATTR_UID &&
 314             !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
 315                 return -EOVERFLOW;
 316         if (ia_valid & ATTR_GID &&
 317             !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
 318                 return -EOVERFLOW;
 319
 320         /* Don't allow modifications of files with invalid uids or
 321          * gids unless those uids & gids are being made valid.
 322          */
 323         if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
 324                 return -EOVERFLOW;
 325         if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
 326                 return -EOVERFLOW;
 327
 328         error = security_inode_setattr(dentry, attr);
 329         if (error)
 330                 return error;
 331         error = try_break_deleg(inode, delegated_inode);
 332         if (error)
 333                 return error;
 334
 335         if (inode->i_op->setattr)
 336                 error = inode->i_op->setattr(dentry, attr);
 337         else
 338                 error = simple_setattr(dentry, attr);
 339
 340         if (!error) {
 341                 fsnotify_change(dentry, ia_valid);
 342                 ima_inode_post_setattr(dentry);
 343                 evm_inode_post_setattr(dentry, ia_valid);
 344         }
 345
 346         return error;
 347 }
 348 EXPORT_SYMBOL(notify_change);