linux/fs/attr.c
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   1/*
   2 *  linux/fs/attr.c
   3 *
   4 *  Copyright (C) 1991, 1992  Linus Torvalds
   5 *  changes by Thomas Schoebel-Theuer
   6 */
   7
   8#include <linux/module.h>
   9#include <linux/time.h>
  10#include <linux/mm.h>
  11#include <linux/string.h>
  12#include <linux/capability.h>
  13#include <linux/fsnotify.h>
  14#include <linux/fcntl.h>
  15#include <linux/security.h>
  16
  17/**
  18 * inode_change_ok - check if attribute changes to an inode are allowed
  19 * @inode:      inode to check
  20 * @attr:       attributes to change
  21 *
  22 * Check if we are allowed to change the attributes contained in @attr
  23 * in the given inode.  This includes the normal unix access permission
  24 * checks, as well as checks for rlimits and others.
  25 *
  26 * Should be called as the first thing in ->setattr implementations,
  27 * possibly after taking additional locks.
  28 */
  29int inode_change_ok(const struct inode *inode, struct iattr *attr)
  30{
  31        unsigned int ia_valid = attr->ia_valid;
  32
  33        /*
  34         * First check size constraints.  These can't be overriden using
  35         * ATTR_FORCE.
  36         */
  37        if (ia_valid & ATTR_SIZE) {
  38                int error = inode_newsize_ok(inode, attr->ia_size);
  39                if (error)
  40                        return error;
  41        }
  42
  43        /* If force is set do it anyway. */
  44        if (ia_valid & ATTR_FORCE)
  45                return 0;
  46
  47        /* Make sure a caller can chown. */
  48        if ((ia_valid & ATTR_UID) &&
  49            (current_fsuid() != inode->i_uid ||
  50             attr->ia_uid != inode->i_uid) && !capable(CAP_CHOWN))
  51                return -EPERM;
  52
  53        /* Make sure caller can chgrp. */
  54        if ((ia_valid & ATTR_GID) &&
  55            (current_fsuid() != inode->i_uid ||
  56            (!in_group_p(attr->ia_gid) && attr->ia_gid != inode->i_gid)) &&
  57            !capable(CAP_CHOWN))
  58                return -EPERM;
  59
  60        /* Make sure a caller can chmod. */
  61        if (ia_valid & ATTR_MODE) {
  62                if (!inode_owner_or_capable(inode))
  63                        return -EPERM;
  64                /* Also check the setgid bit! */
  65                if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  66                                inode->i_gid) && !capable(CAP_FSETID))
  67                        attr->ia_mode &= ~S_ISGID;
  68        }
  69
  70        /* Check for setting the inode time. */
  71        if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
  72                if (!inode_owner_or_capable(inode))
  73                        return -EPERM;
  74        }
  75
  76        return 0;
  77}
  78EXPORT_SYMBOL(inode_change_ok);
  79
  80/**
  81 * inode_newsize_ok - may this inode be truncated to a given size
  82 * @inode:      the inode to be truncated
  83 * @offset:     the new size to assign to the inode
  84 * @Returns:    0 on success, -ve errno on failure
  85 *
  86 * inode_newsize_ok must be called with i_mutex held.
  87 *
  88 * inode_newsize_ok will check filesystem limits and ulimits to check that the
  89 * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
  90 * when necessary. Caller must not proceed with inode size change if failure is
  91 * returned. @inode must be a file (not directory), with appropriate
  92 * permissions to allow truncate (inode_newsize_ok does NOT check these
  93 * conditions).
  94 */
  95int inode_newsize_ok(const struct inode *inode, loff_t offset)
  96{
  97        if (inode->i_size < offset) {
  98                unsigned long limit;
  99
 100                limit = rlimit(RLIMIT_FSIZE);
 101                if (limit != RLIM_INFINITY && offset > limit)
 102                        goto out_sig;
 103                if (offset > inode->i_sb->s_maxbytes)
 104                        goto out_big;
 105        } else {
 106                /*
 107                 * truncation of in-use swapfiles is disallowed - it would
 108                 * cause subsequent swapout to scribble on the now-freed
 109                 * blocks.
 110                 */
 111                if (IS_SWAPFILE(inode))
 112                        return -ETXTBSY;
 113        }
 114
 115        return 0;
 116out_sig:
 117        send_sig(SIGXFSZ, current, 0);
 118out_big:
 119        return -EFBIG;
 120}
 121EXPORT_SYMBOL(inode_newsize_ok);
 122
 123/**
 124 * setattr_copy - copy simple metadata updates into the generic inode
 125 * @inode:      the inode to be updated
 126 * @attr:       the new attributes
 127 *
 128 * setattr_copy must be called with i_mutex held.
 129 *
 130 * setattr_copy updates the inode's metadata with that specified
 131 * in attr. Noticeably missing is inode size update, which is more complex
 132 * as it requires pagecache updates.
 133 *
 134 * The inode is not marked as dirty after this operation. The rationale is
 135 * that for "simple" filesystems, the struct inode is the inode storage.
 136 * The caller is free to mark the inode dirty afterwards if needed.
 137 */
 138void setattr_copy(struct inode *inode, const struct iattr *attr)
 139{
 140        unsigned int ia_valid = attr->ia_valid;
 141
 142        if (ia_valid & ATTR_UID)
 143                inode->i_uid = attr->ia_uid;
 144        if (ia_valid & ATTR_GID)
 145                inode->i_gid = attr->ia_gid;
 146        if (ia_valid & ATTR_ATIME)
 147                inode->i_atime = timespec_trunc(attr->ia_atime,
 148                                                inode->i_sb->s_time_gran);
 149        if (ia_valid & ATTR_MTIME)
 150                inode->i_mtime = timespec_trunc(attr->ia_mtime,
 151                                                inode->i_sb->s_time_gran);
 152        if (ia_valid & ATTR_CTIME)
 153                inode->i_ctime = timespec_trunc(attr->ia_ctime,
 154                                                inode->i_sb->s_time_gran);
 155        if (ia_valid & ATTR_MODE) {
 156                umode_t mode = attr->ia_mode;
 157
 158                if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
 159                        mode &= ~S_ISGID;
 160                inode->i_mode = mode;
 161        }
 162}
 163EXPORT_SYMBOL(setattr_copy);
 164
 165int notify_change(struct dentry * dentry, struct iattr * attr)
 166{
 167        struct inode *inode = dentry->d_inode;
 168        mode_t mode = inode->i_mode;
 169        int error;
 170        struct timespec now;
 171        unsigned int ia_valid = attr->ia_valid;
 172
 173        if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 174                if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 175                        return -EPERM;
 176        }
 177
 178        if ((ia_valid & ATTR_MODE)) {
 179                mode_t amode = attr->ia_mode;
 180                /* Flag setting protected by i_mutex */
 181                if (is_sxid(amode))
 182                        inode->i_flags &= ~S_NOSEC;
 183        }
 184
 185        now = current_fs_time(inode->i_sb);
 186
 187        attr->ia_ctime = now;
 188        if (!(ia_valid & ATTR_ATIME_SET))
 189                attr->ia_atime = now;
 190        if (!(ia_valid & ATTR_MTIME_SET))
 191                attr->ia_mtime = now;
 192        if (ia_valid & ATTR_KILL_PRIV) {
 193                attr->ia_valid &= ~ATTR_KILL_PRIV;
 194                ia_valid &= ~ATTR_KILL_PRIV;
 195                error = security_inode_need_killpriv(dentry);
 196                if (error > 0)
 197                        error = security_inode_killpriv(dentry);
 198                if (error)
 199                        return error;
 200        }
 201
 202        /*
 203         * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 204         * that the function has the ability to reinterpret a mode change
 205         * that's due to these bits. This adds an implicit restriction that
 206         * no function will ever call notify_change with both ATTR_MODE and
 207         * ATTR_KILL_S*ID set.
 208         */
 209        if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 210            (ia_valid & ATTR_MODE))
 211                BUG();
 212
 213        if (ia_valid & ATTR_KILL_SUID) {
 214                if (mode & S_ISUID) {
 215                        ia_valid = attr->ia_valid |= ATTR_MODE;
 216                        attr->ia_mode = (inode->i_mode & ~S_ISUID);
 217                }
 218        }
 219        if (ia_valid & ATTR_KILL_SGID) {
 220                if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 221                        if (!(ia_valid & ATTR_MODE)) {
 222                                ia_valid = attr->ia_valid |= ATTR_MODE;
 223                                attr->ia_mode = inode->i_mode;
 224                        }
 225                        attr->ia_mode &= ~S_ISGID;
 226                }
 227        }
 228        if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 229                return 0;
 230
 231        error = security_inode_setattr(dentry, attr);
 232        if (error)
 233                return error;
 234
 235        if (inode->i_op->setattr)
 236                error = inode->i_op->setattr(dentry, attr);
 237        else
 238                error = simple_setattr(dentry, attr);
 239
 240        if (!error)
 241                fsnotify_change(dentry, ia_valid);
 242
 243        return error;
 244}
 245
 246EXPORT_SYMBOL(notify_change);
 247
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