// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/attr.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  changes by Thomas Schoebel-Theuer
 */

#include <linux/export.h>
#include <linux/time.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/sched/signal.h>
#include <linux/capability.h>
#include <linux/fsnotify.h>
#include <linux/fcntl.h>
#include <linux/security.h>
#include <linux/evm.h>
#include <linux/ima.h>

/**
 * setattr_prepare - check if attribute changes to a dentry are allowed
 * @dentry:     dentry to check
 * @attr:       attributes to change
 *
 * Check if we are allowed to change the attributes contained in @attr
 * in the given dentry.  This includes the normal unix access permission
 * checks, as well as checks for rlimits and others. The function also clears
 * SGID bit from mode if user is not allowed to set it. Also file capabilities
 * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
 *
 * Should be called as the first thing in ->setattr implementations,
 * possibly after taking additional locks.
 */
int setattr_prepare(struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = d_inode(dentry);
        unsigned int ia_valid = attr->ia_valid;

        /*
         * First check size constraints.  These can't be overriden using
         * ATTR_FORCE.
         */
        if (ia_valid & ATTR_SIZE) {
                int error = inode_newsize_ok(inode, attr->ia_size);
                if (error)
                        return error;
        }

        /* If force is set do it anyway. */
        if (ia_valid & ATTR_FORCE)
                goto kill_priv;

        /* Make sure a caller can chown. */
        if ((ia_valid & ATTR_UID) &&
            (!uid_eq(current_fsuid(), inode->i_uid) ||
             !uid_eq(attr->ia_uid, inode->i_uid)) &&
            !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
                return -EPERM;

        /* Make sure caller can chgrp. */
        if ((ia_valid & ATTR_GID) &&
            (!uid_eq(current_fsuid(), inode->i_uid) ||
            (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
            !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
                return -EPERM;

        /* Make sure a caller can chmod. */
        if (ia_valid & ATTR_MODE) {
                if (!inode_owner_or_capable(inode))
                        return -EPERM;
                /* Also check the setgid bit! */
                if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
                                inode->i_gid) &&
                    !capable_wrt_inode_uidgid(inode, CAP_FSETID))
                        attr->ia_mode &= ~S_ISGID;
        }

        /* Check for setting the inode time. */
        if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
                if (!inode_owner_or_capable(inode))
                        return -EPERM;
        }

kill_priv:
        /* User has permission for the change */
        if (ia_valid & ATTR_KILL_PRIV) {
                int error;

                error = security_inode_killpriv(dentry);
                if (error)
                        return error;
        }

        return 0;
}
EXPORT_SYMBOL(setattr_prepare);

/**
 * inode_newsize_ok - may this inode be truncated to a given size
 * @inode:      the inode to be truncated
 * @offset:     the new size to assign to the inode
 * @Returns:    0 on success, -ve errno on failure
 *
 * inode_newsize_ok must be called with i_mutex held.
 *
 * inode_newsize_ok will check filesystem limits and ulimits to check that the
 * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
 * when necessary. Caller must not proceed with inode size change if failure is
 * returned. @inode must be a file (not directory), with appropriate
 * permissions to allow truncate (inode_newsize_ok does NOT check these
 * conditions).
 */
int inode_newsize_ok(const struct inode *inode, loff_t offset)
{
        if (inode->i_size < offset) {
                unsigned long limit;

                limit = rlimit(RLIMIT_FSIZE);
                if (limit != RLIM_INFINITY && offset > limit)
                        goto out_sig;
                if (offset > inode->i_sb->s_maxbytes)
                        goto out_big;
        } else {
                /*
                 * truncation of in-use swapfiles is disallowed - it would
                 * cause subsequent swapout to scribble on the now-freed
                 * blocks.
                 */
                if (IS_SWAPFILE(inode))
                        return -ETXTBSY;
        }

        return 0;
out_sig:
        send_sig(SIGXFSZ, current, 0);
out_big:
        return -EFBIG;
}
EXPORT_SYMBOL(inode_newsize_ok);

/**
 * setattr_copy - copy simple metadata updates into the generic inode
 * @inode:      the inode to be updated
 * @attr:       the new attributes
 *
 * setattr_copy must be called with i_mutex held.
 *
 * setattr_copy updates the inode's metadata with that specified
 * in attr. Noticeably missing is inode size update, which is more complex
 * as it requires pagecache updates.
 *
 * The inode is not marked as dirty after this operation. The rationale is
 * that for "simple" filesystems, the struct inode is the inode storage.
 * The caller is free to mark the inode dirty afterwards if needed.
 */
void setattr_copy(struct inode *inode, const struct iattr *attr)
{
        unsigned int ia_valid = attr->ia_valid;

        if (ia_valid & ATTR_UID)
                inode->i_uid = attr->ia_uid;
        if (ia_valid & ATTR_GID)
                inode->i_gid = attr->ia_gid;
        if (ia_valid & ATTR_ATIME)
                inode->i_atime = timespec_trunc(attr->ia_atime,
                                                inode->i_sb->s_time_gran);
        if (ia_valid & ATTR_MTIME)
                inode->i_mtime = timespec_trunc(attr->ia_mtime,
                                                inode->i_sb->s_time_gran);
        if (ia_valid & ATTR_CTIME)
                inode->i_ctime = timespec_trunc(attr->ia_ctime,
                                                inode->i_sb->s_time_gran);
        if (ia_valid & ATTR_MODE) {
                umode_t mode = attr->ia_mode;

                if (!in_group_p(inode->i_gid) &&
                    !capable_wrt_inode_uidgid(inode, CAP_FSETID))
                        mode &= ~S_ISGID;
                inode->i_mode = mode;
        }
}
EXPORT_SYMBOL(setattr_copy);

/**
 * notify_change - modify attributes of a filesytem object
 * @dentry:     object affected
 * @iattr:      new attributes
 * @delegated_inode: returns inode, if the inode is delegated
 *
 * The caller must hold the i_mutex on the affected object.
 *
 * If notify_change discovers a delegation in need of breaking,
 * it will return -EWOULDBLOCK and return a reference to the inode in
 * delegated_inode.  The caller should then break the delegation and
 * retry.  Because breaking a delegation may take a long time, the
 * caller should drop the i_mutex before doing so.
 *
 * Alternatively, a caller may pass NULL for delegated_inode.  This may
 * be appropriate for callers that expect the underlying filesystem not
 * to be NFS exported.  Also, passing NULL is fine for callers holding
 * the file open for write, as there can be no conflicting delegation in
 * that case.
 */
int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
{
        struct inode *inode = dentry->d_inode;
        umode_t mode = inode->i_mode;
        int error;
        struct timespec now;
        unsigned int ia_valid = attr->ia_valid;

        WARN_ON_ONCE(!inode_is_locked(inode));

        if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
                if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
                        return -EPERM;
        }

        /*
         * If utimes(2) and friends are called with times == NULL (or both
         * times are UTIME_NOW), then we need to check for write permission
         */
        if (ia_valid & ATTR_TOUCH) {
                if (IS_IMMUTABLE(inode))
                        return -EPERM;

                if (!inode_owner_or_capable(inode)) {
                        error = inode_permission(inode, MAY_WRITE);
                        if (error)
                                return error;
                }
        }

        if ((ia_valid & ATTR_MODE)) {
                umode_t amode = attr->ia_mode;
                /* Flag setting protected by i_mutex */
                if (is_sxid(amode))
                        inode->i_flags &= ~S_NOSEC;
        }

        now = current_time(inode);

        attr->ia_ctime = now;
        if (!(ia_valid & ATTR_ATIME_SET))
                attr->ia_atime = now;
        if (!(ia_valid & ATTR_MTIME_SET))
                attr->ia_mtime = now;
        if (ia_valid & ATTR_KILL_PRIV) {
                error = security_inode_need_killpriv(dentry);
                if (error < 0)
                        return error;
                if (error == 0)
                        ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
        }

        /*
         * We now pass ATTR_KILL_S*ID to the lower level setattr function so
         * that the function has the ability to reinterpret a mode change
         * that's due to these bits. This adds an implicit restriction that
         * no function will ever call notify_change with both ATTR_MODE and
         * ATTR_KILL_S*ID set.
         */
        if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
            (ia_valid & ATTR_MODE))
                BUG();

        if (ia_valid & ATTR_KILL_SUID) {
                if (mode & S_ISUID) {
                        ia_valid = attr->ia_valid |= ATTR_MODE;
                        attr->ia_mode = (inode->i_mode & ~S_ISUID);
                }
        }
        if (ia_valid & ATTR_KILL_SGID) {
                if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
                        if (!(ia_valid & ATTR_MODE)) {
                                ia_valid = attr->ia_valid |= ATTR_MODE;
                                attr->ia_mode = inode->i_mode;
                        }
                        attr->ia_mode &= ~S_ISGID;
                }
        }
        if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
                return 0;

        /*
         * Verify that uid/gid changes are valid in the target
         * namespace of the superblock.
         */
        if (ia_valid & ATTR_UID &&
            !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
                return -EOVERFLOW;
        if (ia_valid & ATTR_GID &&
            !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
                return -EOVERFLOW;

        /* Don't allow modifications of files with invalid uids or
         * gids unless those uids & gids are being made valid.
         */
        if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
                return -EOVERFLOW;
        if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
                return -EOVERFLOW;

        error = security_inode_setattr(dentry, attr);
        if (error)
                return error;
        error = try_break_deleg(inode, delegated_inode);
        if (error)
                return error;

        if (inode->i_op->setattr)
                error = inode->i_op->setattr(dentry, attr);
        else
                error = simple_setattr(dentry, attr);

        if (!error) {
                fsnotify_change(dentry, ia_valid);
                ima_inode_post_setattr(dentry);
                evm_inode_post_setattr(dentry, ia_valid);
        }

        return error;
}
EXPORT_SYMBOL(notify_change);