posix_acl.c

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/*
 * linux/fs/posix_acl.c
 *
 *  Copyright (C) 2002 by Andreas Gruenbacher <[email protected]>
 *
 *  Fixes from William Schumacher incorporated on 15 March 2001.
 *     (Reported by Charles Bertsch, <[email protected]>).
 */

/*
 *  This file contains generic functions for manipulating
 *  POSIX 1003.1e draft standard 17 ACLs.
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/atomic.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/posix_acl.h>
#include <linux/export.h>

#include <linux/errno.h>

EXPORT_SYMBOL(posix_acl_init);
EXPORT_SYMBOL(posix_acl_alloc);
EXPORT_SYMBOL(posix_acl_valid);
EXPORT_SYMBOL(posix_acl_equiv_mode);
EXPORT_SYMBOL(posix_acl_from_mode);

/*
 * Init a fresh posix_acl
 */
void
posix_acl_init(struct posix_acl *acl, int count)
{
    atomic_set(&acl->a_refcount, 1);
    acl->a_count = count;
}

/*
 * Allocate a new ACL with the specified number of entries.
 */
struct posix_acl *
posix_acl_alloc(int count, gfp_t flags)
{
    const size_t size = sizeof(struct posix_acl) +
                        count * sizeof(struct posix_acl_entry);
    struct posix_acl *acl = kmalloc(size, flags);
    if (acl)
        posix_acl_init(acl, count);
    return acl;
}

/*
 * Clone an ACL.
 */
static struct posix_acl *
posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
{
    struct posix_acl *clone = NULL;

    if (acl) {
        int size = sizeof(struct posix_acl) + acl->a_count *
                   sizeof(struct posix_acl_entry);
        clone = kmemdup(acl, size, flags);
        if (clone)
            atomic_set(&clone->a_refcount, 1);
    }
    return clone;
}

/*
 * Check if an acl is valid. Returns 0 if it is, or -E... otherwise.
 */
int
posix_acl_valid(const struct posix_acl *acl)
{
    const struct posix_acl_entry *pa, *pe;
    int state = ACL_USER_OBJ;
    kuid_t prev_uid = INVALID_UID;
    kgid_t prev_gid = INVALID_GID;
    int needs_mask = 0;

    FOREACH_ACL_ENTRY(pa, acl, pe) {
        if (pa->e_perm & ~(ACL_READ|ACL_WRITE|ACL_EXECUTE))
            return -EINVAL;
        switch (pa->e_tag) {
            case ACL_USER_OBJ:
                if (state == ACL_USER_OBJ) {
                    state = ACL_USER;
                    break;
                }
                return -EINVAL;

            case ACL_USER:
                if (state != ACL_USER)
                    return -EINVAL;
                if (!uid_valid(pa->e_uid))
                    return -EINVAL;
                if (uid_valid(prev_uid) &&
                    uid_lte(pa->e_uid, prev_uid))
                    return -EINVAL;
                prev_uid = pa->e_uid;
                needs_mask = 1;
                break;

            case ACL_GROUP_OBJ:
                if (state == ACL_USER) {
                    state = ACL_GROUP;
                    break;
                }
                return -EINVAL;

            case ACL_GROUP:
                if (state != ACL_GROUP)
                    return -EINVAL;
                if (!gid_valid(pa->e_gid))
                    return -EINVAL;
                if (gid_valid(prev_gid) &&
                    gid_lte(pa->e_gid, prev_gid))
                    return -EINVAL;
                prev_gid = pa->e_gid;
                needs_mask = 1;
                break;

            case ACL_MASK:
                if (state != ACL_GROUP)
                    return -EINVAL;
                state = ACL_OTHER;
                break;

            case ACL_OTHER:
                if (state == ACL_OTHER ||
                    (state == ACL_GROUP && !needs_mask)) {
                    state = 0;
                    break;
                }
                return -EINVAL;

            default:
                return -EINVAL;
        }
    }
    if (state == 0)
        return 0;
    return -EINVAL;
}

/*
 * Returns 0 if the acl can be exactly represented in the traditional
 * file mode permission bits, or else 1. Returns -E... on error.
 */
int
posix_acl_equiv_mode(const struct posix_acl *acl, umode_t *mode_p)
{
    const struct posix_acl_entry *pa, *pe;
    umode_t mode = 0;
    int not_equiv = 0;

    FOREACH_ACL_ENTRY(pa, acl, pe) {
        switch (pa->e_tag) {
            case ACL_USER_OBJ:
                mode |= (pa->e_perm & S_IRWXO) << 6;
                break;
            case ACL_GROUP_OBJ:
                mode |= (pa->e_perm & S_IRWXO) << 3;
                break;
            case ACL_OTHER:
                mode |= pa->e_perm & S_IRWXO;
                break;
            case ACL_MASK:
                mode = (mode & ~S_IRWXG) |
                       ((pa->e_perm & S_IRWXO) << 3);
                not_equiv = 1;
                break;
            case ACL_USER:
            case ACL_GROUP:
                not_equiv = 1;
                break;
            default:
                return -EINVAL;
        }
    }
        if (mode_p)
                *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
        return not_equiv;
}

/*
 * Create an ACL representing the file mode permission bits of an inode.
 */
struct posix_acl *
posix_acl_from_mode(umode_t mode, gfp_t flags)
{
    struct posix_acl *acl = posix_acl_alloc(3, flags);
    if (!acl)
        return ERR_PTR(-ENOMEM);

    acl->a_entries[0].e_tag  = ACL_USER_OBJ;
    acl->a_entries[0].e_perm = (mode & S_IRWXU) >> 6;

    acl->a_entries[1].e_tag  = ACL_GROUP_OBJ;
    acl->a_entries[1].e_perm = (mode & S_IRWXG) >> 3;

    acl->a_entries[2].e_tag  = ACL_OTHER;
    acl->a_entries[2].e_perm = (mode & S_IRWXO);
    return acl;
}

/*
 * Return 0 if current is granted want access to the inode
 * by the acl. Returns -E... otherwise.
 */
int
posix_acl_permission(struct inode *inode, const struct posix_acl *acl, int want)
{
    const struct posix_acl_entry *pa, *pe, *mask_obj;
    int found = 0;

    want &= MAY_READ | MAY_WRITE | MAY_EXEC | MAY_NOT_BLOCK;

    FOREACH_ACL_ENTRY(pa, acl, pe) {
                switch(pa->e_tag) {
                        case ACL_USER_OBJ:
                /* (May have been checked already) */
                if (uid_eq(inode->i_uid, current_fsuid()))
                                        goto check_perm;
                                break;
                        case ACL_USER:
                if (uid_eq(pa->e_uid, current_fsuid()))
                                        goto mask;
                break;
                        case ACL_GROUP_OBJ:
                                if (in_group_p(inode->i_gid)) {
                    found = 1;
                    if ((pa->e_perm & want) == want)
                        goto mask;
                                }
                break;
                        case ACL_GROUP:
                if (in_group_p(pa->e_gid)) {
                    found = 1;
                    if ((pa->e_perm & want) == want)
                        goto mask;
                                }
                                break;
                        case ACL_MASK:
                                break;
                        case ACL_OTHER:
                if (found)
                    return -EACCES;
                else
                    goto check_perm;
            default:
                return -EIO;
                }
        }
    return -EIO;

mask:
    for (mask_obj = pa+1; mask_obj != pe; mask_obj++) {
        if (mask_obj->e_tag == ACL_MASK) {
            if ((pa->e_perm & mask_obj->e_perm & want) == want)
                return 0;
            return -EACCES;
        }
    }

check_perm:
    if ((pa->e_perm & want) == want)
        return 0;
    return -EACCES;
}

/*
 * Modify acl when creating a new inode. The caller must ensure the acl is
 * only referenced once.
 *
 * mode_p initially must contain the mode parameter to the open() / creat()
 * system calls. All permissions that are not granted by the acl are removed.
 * The permissions in the acl are changed to reflect the mode_p parameter.
 */
static int posix_acl_create_masq(struct posix_acl *acl, umode_t *mode_p)
{
    struct posix_acl_entry *pa, *pe;
    struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
    umode_t mode = *mode_p;
    int not_equiv = 0;

    /* assert(atomic_read(acl->a_refcount) == 1); */

    FOREACH_ACL_ENTRY(pa, acl, pe) {
                switch(pa->e_tag) {
                        case ACL_USER_OBJ:
                pa->e_perm &= (mode >> 6) | ~S_IRWXO;
                mode &= (pa->e_perm << 6) | ~S_IRWXU;
                break;

            case ACL_USER:
            case ACL_GROUP:
                not_equiv = 1;
                break;

                        case ACL_GROUP_OBJ:
                group_obj = pa;
                                break;

                        case ACL_OTHER:
                pa->e_perm &= mode | ~S_IRWXO;
                mode &= pa->e_perm | ~S_IRWXO;
                                break;

                        case ACL_MASK:
                mask_obj = pa;
                not_equiv = 1;
                                break;

            default:
                return -EIO;
                }
        }

    if (mask_obj) {
        mask_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
        mode &= (mask_obj->e_perm << 3) | ~S_IRWXG;
    } else {
        if (!group_obj)
            return -EIO;
        group_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
        mode &= (group_obj->e_perm << 3) | ~S_IRWXG;
    }

    *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
        return not_equiv;
}

/*
 * Modify the ACL for the chmod syscall.
 */
static int posix_acl_chmod_masq(struct posix_acl *acl, umode_t mode)
{
    struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
    struct posix_acl_entry *pa, *pe;

    /* assert(atomic_read(acl->a_refcount) == 1); */

    FOREACH_ACL_ENTRY(pa, acl, pe) {
        switch(pa->e_tag) {
            case ACL_USER_OBJ:
                pa->e_perm = (mode & S_IRWXU) >> 6;
                break;

            case ACL_USER:
            case ACL_GROUP:
                break;

            case ACL_GROUP_OBJ:
                group_obj = pa;
                break;

            case ACL_MASK:
                mask_obj = pa;
                break;

            case ACL_OTHER:
                pa->e_perm = (mode & S_IRWXO);
                break;

            default:
                return -EIO;
        }
    }

    if (mask_obj) {
        mask_obj->e_perm = (mode & S_IRWXG) >> 3;
    } else {
        if (!group_obj)
            return -EIO;
        group_obj->e_perm = (mode & S_IRWXG) >> 3;
    }

    return 0;
}

int
posix_acl_create(struct posix_acl **acl, gfp_t gfp, umode_t *mode_p)
{
    struct posix_acl *clone = posix_acl_clone(*acl, gfp);
    int err = -ENOMEM;
    if (clone) {
        err = posix_acl_create_masq(clone, mode_p);
        if (err < 0) {
            posix_acl_release(clone);
            clone = NULL;
        }
    }
    posix_acl_release(*acl);
    *acl = clone;
    return err;
}
EXPORT_SYMBOL(posix_acl_create);

int
posix_acl_chmod(struct posix_acl **acl, gfp_t gfp, umode_t mode)
{
    struct posix_acl *clone = posix_acl_clone(*acl, gfp);
    int err = -ENOMEM;
    if (clone) {
        err = posix_acl_chmod_masq(clone, mode);
        if (err) {
            posix_acl_release(clone);
            clone = NULL;
        }
    }
    posix_acl_release(*acl);
    *acl = clone;
    return err;
}
EXPORT_SYMBOL(posix_acl_chmod);