subr_acl_posix1e.c

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/*-
 * Copyright (c) 1999-2006 Robert N. M. Watson
 * All rights reserved.
 *
 * This software was developed by Robert Watson for the TrustedBSD Project.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 * Developed by the TrustedBSD Project.
 *
 * ACL support routines specific to POSIX.1e access control lists.  These are
 * utility routines for code common across file systems implementing POSIX.1e
 * ACLs.
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mount.h>
#include <sys/priv.h>
#include <sys/vnode.h>
#include <sys/errno.h>
#include <sys/stat.h>
#include <sys/acl.h>

/*
 * Implement a version of vaccess() that understands POSIX.1e ACL semantics;
 * the access ACL has already been prepared for evaluation by the file system
 * and is passed via 'uid', 'gid', and 'acl'.  Return 0 on success, else an
 * errno value.
 */
int
vaccess_acl_posix1e(enum vtype type, uid_t file_uid, gid_t file_gid,
    struct acl *acl, accmode_t accmode, struct ucred *cred, int *privused)
{
        struct acl_entry *acl_other, *acl_mask;
        accmode_t dac_granted;
        accmode_t priv_granted;
        accmode_t acl_mask_granted;
        int group_matched, i;

        KASSERT((accmode & ~(VEXEC | VWRITE | VREAD | VADMIN | VAPPEND)) == 0,
            ("invalid bit in accmode"));
        KASSERT((accmode & VAPPEND) == 0 || (accmode & VWRITE),
                ("VAPPEND without VWRITE"));

        /*
         * Look for a normal, non-privileged way to access the file/directory
         * as requested.  If it exists, go with that.  Otherwise, attempt to
         * use privileges granted via priv_granted.  In some cases, which
         * privileges to use may be ambiguous due to "best match", in which
         * case fall back on first match for the time being.
         */
        if (privused != NULL)
                *privused = 0;

        /*
         * Determine privileges now, but don't apply until we've found a DAC
         * entry that matches but has failed to allow access.
         *
         * XXXRW: Ideally, we'd determine the privileges required before
         * asking for them.
         */
        priv_granted = 0;

        if (type == VDIR) {
                if ((accmode & VEXEC) && !priv_check_cred(cred,
                     PRIV_VFS_LOOKUP, 0))
                        priv_granted |= VEXEC;
        } else {
                /*
                 * Ensure that at least one execute bit is on. Otherwise,
                 * a privileged user will always succeed, and we don't want
                 * this to happen unless the file really is executable.
                 */
                if ((accmode & VEXEC) && (acl_posix1e_acl_to_mode(acl) &
                    (S_IXUSR | S_IXGRP | S_IXOTH)) != 0 &&
                    !priv_check_cred(cred, PRIV_VFS_EXEC, 0))
                        priv_granted |= VEXEC;
        }

        if ((accmode & VREAD) && !priv_check_cred(cred, PRIV_VFS_READ, 0))
                priv_granted |= VREAD;

        if (((accmode & VWRITE) || (accmode & VAPPEND)) &&
            !priv_check_cred(cred, PRIV_VFS_WRITE, 0))
                priv_granted |= (VWRITE | VAPPEND);

        if ((accmode & VADMIN) && !priv_check_cred(cred, PRIV_VFS_ADMIN, 0))
                priv_granted |= VADMIN;

        /*
         * The owner matches if the effective uid associated with the
         * credential matches that of the ACL_USER_OBJ entry.  While we're
         * doing the first scan, also cache the location of the ACL_MASK and
         * ACL_OTHER entries, preventing some future iterations.
         */
        acl_mask = acl_other = NULL;
        for (i = 0; i < acl->acl_cnt; i++) {
                switch (acl->acl_entry[i].ae_tag) {
                case ACL_USER_OBJ:
                        if (file_uid != cred->cr_uid)
                                break;
                        dac_granted = 0;
                        dac_granted |= VADMIN;
                        if (acl->acl_entry[i].ae_perm & ACL_EXECUTE)
                                dac_granted |= VEXEC;
                        if (acl->acl_entry[i].ae_perm & ACL_READ)
                                dac_granted |= VREAD;
                        if (acl->acl_entry[i].ae_perm & ACL_WRITE)
                                dac_granted |= (VWRITE | VAPPEND);
                        if ((accmode & dac_granted) == accmode)
                                return (0);

                        /*
                         * XXXRW: Do privilege lookup here.
                         */
                        if ((accmode & (dac_granted | priv_granted)) ==
                            accmode) {
                                if (privused != NULL)
                                        *privused = 1;
                                return (0);
                        }
                        goto error;

                case ACL_MASK:
                        acl_mask = &acl->acl_entry[i];
                        break;

                case ACL_OTHER:
                        acl_other = &acl->acl_entry[i];
                        break;

                default:
                        break;
                }
        }

        /*
         * An ACL_OTHER entry should always exist in a valid access ACL.  If
         * it doesn't, then generate a serious failure.  For now, this means
         * a debugging message and EPERM, but in the future should probably
         * be a panic.
         */
        if (acl_other == NULL) {
                /*
                 * XXX This should never happen
                 */
                printf("vaccess_acl_posix1e: ACL_OTHER missing\n");
                return (EPERM);
        }

        /*
         * Checks against ACL_USER, ACL_GROUP_OBJ, and ACL_GROUP fields are
         * masked by an ACL_MASK entry, if any.  As such, first identify the
         * ACL_MASK field, then iterate through identifying potential user
         * matches, then group matches.  If there is no ACL_MASK, assume that
         * the mask allows all requests to succeed.
         */
        if (acl_mask != NULL) {
                acl_mask_granted = 0;
                if (acl_mask->ae_perm & ACL_EXECUTE)
                        acl_mask_granted |= VEXEC;
                if (acl_mask->ae_perm & ACL_READ)
                        acl_mask_granted |= VREAD;
                if (acl_mask->ae_perm & ACL_WRITE)
                        acl_mask_granted |= (VWRITE | VAPPEND);
        } else
                acl_mask_granted = VEXEC | VREAD | VWRITE | VAPPEND;

        /*
         * Check ACL_USER ACL entries.  There will either be one or no
         * matches; if there is one, we accept or rejected based on the
         * match; otherwise, we continue on to groups.
         */
        for (i = 0; i < acl->acl_cnt; i++) {
                switch (acl->acl_entry[i].ae_tag) {
                case ACL_USER:
                        if (acl->acl_entry[i].ae_id != cred->cr_uid)
                                break;
                        dac_granted = 0;
                        if (acl->acl_entry[i].ae_perm & ACL_EXECUTE)
                                dac_granted |= VEXEC;
                        if (acl->acl_entry[i].ae_perm & ACL_READ)
                                dac_granted |= VREAD;
                        if (acl->acl_entry[i].ae_perm & ACL_WRITE)
                                dac_granted |= (VWRITE | VAPPEND);
                        dac_granted &= acl_mask_granted;
                        if ((accmode & dac_granted) == accmode)
                                return (0);
                        /*
                         * XXXRW: Do privilege lookup here.
                         */
                        if ((accmode & (dac_granted | priv_granted)) !=
                            accmode)
                                goto error;

                        if (privused != NULL)
                                *privused = 1;
                        return (0);
                }
        }

        /*
         * Group match is best-match, not first-match, so find a "best"
         * match.  Iterate across, testing each potential group match.  Make
         * sure we keep track of whether we found a match or not, so that we
         * know if we should try again with any available privilege, or if we
         * should move on to ACL_OTHER.
         */
        group_matched = 0;
        for (i = 0; i < acl->acl_cnt; i++) {
                switch (acl->acl_entry[i].ae_tag) {
                case ACL_GROUP_OBJ:
                        if (!groupmember(file_gid, cred))
                                break;
                        dac_granted = 0;
                        if (acl->acl_entry[i].ae_perm & ACL_EXECUTE)
                                dac_granted |= VEXEC;
                        if (acl->acl_entry[i].ae_perm & ACL_READ)
                                dac_granted |= VREAD;
                        if (acl->acl_entry[i].ae_perm & ACL_WRITE)
                                dac_granted |= (VWRITE | VAPPEND);
                        dac_granted  &= acl_mask_granted;

                        if ((accmode & dac_granted) == accmode)
                                return (0);

                        group_matched = 1;
                        break;

                case ACL_GROUP:
                        if (!groupmember(acl->acl_entry[i].ae_id, cred))
                                break;
                        dac_granted = 0;
                        if (acl->acl_entry[i].ae_perm & ACL_EXECUTE)
                                dac_granted |= VEXEC;
                        if (acl->acl_entry[i].ae_perm & ACL_READ)
                                dac_granted |= VREAD;
                        if (acl->acl_entry[i].ae_perm & ACL_WRITE)
                                dac_granted |= (VWRITE | VAPPEND);
                        dac_granted  &= acl_mask_granted;

                        if ((accmode & dac_granted) == accmode)
                                return (0);

                        group_matched = 1;
                        break;

                default:
                        break;
                }
        }

        if (group_matched == 1) {
                /*
                 * There was a match, but it did not grant rights via pure
                 * DAC.  Try again, this time with privilege.
                 */
                for (i = 0; i < acl->acl_cnt; i++) {
                        switch (acl->acl_entry[i].ae_tag) {
                        case ACL_GROUP_OBJ:
                                if (!groupmember(file_gid, cred))
                                        break;
                                dac_granted = 0;
                                if (acl->acl_entry[i].ae_perm & ACL_EXECUTE)
                                        dac_granted |= VEXEC;
                                if (acl->acl_entry[i].ae_perm & ACL_READ)
                                        dac_granted |= VREAD;
                                if (acl->acl_entry[i].ae_perm & ACL_WRITE)
                                        dac_granted |= (VWRITE | VAPPEND);
                                dac_granted &= acl_mask_granted;

                                /*
                                 * XXXRW: Do privilege lookup here.
                                 */
                                if ((accmode & (dac_granted | priv_granted))
                                    != accmode)
                                        break;

                                if (privused != NULL)
                                        *privused = 1;
                                return (0);

                        case ACL_GROUP:
                                if (!groupmember(acl->acl_entry[i].ae_id,
                                    cred))
                                        break;
                                dac_granted = 0;
                                if (acl->acl_entry[i].ae_perm & ACL_EXECUTE)
                                dac_granted |= VEXEC;
                                if (acl->acl_entry[i].ae_perm & ACL_READ)
                                        dac_granted |= VREAD;
                                if (acl->acl_entry[i].ae_perm & ACL_WRITE)
                                        dac_granted |= (VWRITE | VAPPEND);
                                dac_granted &= acl_mask_granted;

                                /*
                                 * XXXRW: Do privilege lookup here.
                                 */
                                if ((accmode & (dac_granted | priv_granted))
                                    != accmode)
                                        break;

                                if (privused != NULL)
                                        *privused = 1;
                                return (0);

                        default:
                                break;
                        }
                }
                /*
                 * Even with privilege, group membership was not sufficient.
                 * Return failure.
                 */
                goto error;
        }
                
        /*
         * Fall back on ACL_OTHER.  ACL_MASK is not applied to ACL_OTHER.
         */
        dac_granted = 0;
        if (acl_other->ae_perm & ACL_EXECUTE)
                dac_granted |= VEXEC;
        if (acl_other->ae_perm & ACL_READ)
                dac_granted |= VREAD;
        if (acl_other->ae_perm & ACL_WRITE)
                dac_granted |= (VWRITE | VAPPEND);

        if ((accmode & dac_granted) == accmode)
                return (0);
        /*
         * XXXRW: Do privilege lookup here.
         */
        if ((accmode & (dac_granted | priv_granted)) == accmode) {
                if (privused != NULL)
                        *privused = 1;
                return (0);
        }

error:
        return ((accmode & VADMIN) ? EPERM : EACCES);
}

/*
 * For the purposes of filesystems maintaining the _OBJ entries in an inode
 * with a mode_t field, this routine converts a mode_t entry to an
 * acl_perm_t.
 */
acl_perm_t
acl_posix1e_mode_to_perm(acl_tag_t tag, mode_t mode)
{
        acl_perm_t      perm = 0;

        switch(tag) {
        case ACL_USER_OBJ:
                if (mode & S_IXUSR)
                        perm |= ACL_EXECUTE;
                if (mode & S_IRUSR)
                        perm |= ACL_READ;
                if (mode & S_IWUSR)
                        perm |= ACL_WRITE;
                return (perm);

        case ACL_GROUP_OBJ:
                if (mode & S_IXGRP)
                        perm |= ACL_EXECUTE;
                if (mode & S_IRGRP)
                        perm |= ACL_READ;
                if (mode & S_IWGRP)
                        perm |= ACL_WRITE;
                return (perm);

        case ACL_OTHER:
                if (mode & S_IXOTH)
                        perm |= ACL_EXECUTE;
                if (mode & S_IROTH)
                        perm |= ACL_READ;
                if (mode & S_IWOTH)
                        perm |= ACL_WRITE;
                return (perm);

        default:
                printf("acl_posix1e_mode_to_perm: invalid tag (%d)\n", tag);
                return (0);
        }
}

/*
 * Given inode information (uid, gid, mode), return an acl entry of the
 * appropriate type.
 */
struct acl_entry
acl_posix1e_mode_to_entry(acl_tag_t tag, uid_t uid, gid_t gid, mode_t mode)
{
        struct acl_entry        acl_entry;

        acl_entry.ae_tag = tag;
        acl_entry.ae_perm = acl_posix1e_mode_to_perm(tag, mode);
        acl_entry.ae_entry_type = 0;
        acl_entry.ae_flags = 0;
        switch(tag) {
        case ACL_USER_OBJ:
                acl_entry.ae_id = uid;
                break;

        case ACL_GROUP_OBJ:
                acl_entry.ae_id = gid;
                break;

        case ACL_OTHER:
                acl_entry.ae_id = ACL_UNDEFINED_ID;
                break;

        default:
                acl_entry.ae_id = ACL_UNDEFINED_ID;
                printf("acl_posix1e_mode_to_entry: invalid tag (%d)\n", tag);
        }

        return (acl_entry);
}

/*
 * Utility function to generate a file mode given appropriate ACL entries.
 */
mode_t
acl_posix1e_perms_to_mode(struct acl_entry *acl_user_obj_entry,
    struct acl_entry *acl_group_obj_entry, struct acl_entry *acl_other_entry)
{
        mode_t  mode;

        mode = 0;
        if (acl_user_obj_entry->ae_perm & ACL_EXECUTE)
                mode |= S_IXUSR;
        if (acl_user_obj_entry->ae_perm & ACL_READ)
                mode |= S_IRUSR;
        if (acl_user_obj_entry->ae_perm & ACL_WRITE)
                mode |= S_IWUSR;
        if (acl_group_obj_entry->ae_perm & ACL_EXECUTE)
                mode |= S_IXGRP;
        if (acl_group_obj_entry->ae_perm & ACL_READ)
                mode |= S_IRGRP;
        if (acl_group_obj_entry->ae_perm & ACL_WRITE)
                mode |= S_IWGRP;
        if (acl_other_entry->ae_perm & ACL_EXECUTE)
                mode |= S_IXOTH;
        if (acl_other_entry->ae_perm & ACL_READ)
                mode |= S_IROTH;
        if (acl_other_entry->ae_perm & ACL_WRITE)
                mode |= S_IWOTH;

        return (mode);
}

/*
 * Utility function to generate a file mode given a complete POSIX.1e access
 * ACL.  Note that if the ACL is improperly formed, this may result in a
 * panic.
 */
mode_t
acl_posix1e_acl_to_mode(struct acl *acl)
{
        struct acl_entry *acl_mask, *acl_user_obj, *acl_group_obj, *acl_other;
        int i;

        /*
         * Find the ACL entries relevant to a POSIX permission mode.
         */
        acl_user_obj = acl_group_obj = acl_other = acl_mask = NULL;
        for (i = 0; i < acl->acl_cnt; i++) {
                switch (acl->acl_entry[i].ae_tag) {
                case ACL_USER_OBJ:
                        acl_user_obj = &acl->acl_entry[i];
                        break;

                case ACL_GROUP_OBJ:
                        acl_group_obj = &acl->acl_entry[i];
                        break;

                case ACL_OTHER:
                        acl_other = &acl->acl_entry[i];
                        break;

                case ACL_MASK:
                        acl_mask = &acl->acl_entry[i];
                        break;

                case ACL_USER:
                case ACL_GROUP:
                        break;

                default:
                        panic("acl_posix1e_acl_to_mode: bad ae_tag");
                }
        }

        if (acl_user_obj == NULL || acl_group_obj == NULL || acl_other == NULL)
                panic("acl_posix1e_acl_to_mode: missing base ae_tags");

        /*
         * POSIX.1e specifies that if there is an ACL_MASK entry, we replace
         * the mode "group" bits with its permissions.  If there isn't, we
         * use the ACL_GROUP_OBJ permissions.
         */
        if (acl_mask != NULL)
                return (acl_posix1e_perms_to_mode(acl_user_obj, acl_mask,
                    acl_other));
        else
                return (acl_posix1e_perms_to_mode(acl_user_obj, acl_group_obj,
                    acl_other));
}

/*
 * Perform a syntactic check of the ACL, sufficient to allow an implementing
 * filesystem to determine if it should accept this and rely on the POSIX.1e
 * ACL properties.
 */
int
acl_posix1e_check(struct acl *acl)
{
        int num_acl_user_obj, num_acl_user, num_acl_group_obj, num_acl_group;
        int num_acl_mask, num_acl_other, i;

        /*
         * Verify that the number of entries does not exceed the maximum
         * defined for acl_t.
         *
         * Verify that the correct number of various sorts of ae_tags are
         * present:
         *   Exactly one ACL_USER_OBJ
         *   Exactly one ACL_GROUP_OBJ
         *   Exactly one ACL_OTHER
         *   If any ACL_USER or ACL_GROUP entries appear, then exactly one
         *   ACL_MASK entry must also appear.
         *
         * Verify that all ae_perm entries are in ACL_PERM_BITS.
         *
         * Verify all ae_tag entries are understood by this implementation.
         *
         * Note: Does not check for uniqueness of qualifier (ae_id) field.
         */
        num_acl_user_obj = num_acl_user = num_acl_group_obj = num_acl_group =
            num_acl_mask = num_acl_other = 0;
        if (acl->acl_cnt > ACL_MAX_ENTRIES)
                return (EINVAL);
        for (i = 0; i < acl->acl_cnt; i++) {
                /*
                 * Check for a valid tag.
                 */
                switch(acl->acl_entry[i].ae_tag) {
                case ACL_USER_OBJ:
                        acl->acl_entry[i].ae_id = ACL_UNDEFINED_ID; /* XXX */
                        if (acl->acl_entry[i].ae_id != ACL_UNDEFINED_ID)
                                return (EINVAL);
                        num_acl_user_obj++;
                        break;
                case ACL_GROUP_OBJ:
                        acl->acl_entry[i].ae_id = ACL_UNDEFINED_ID; /* XXX */
                        if (acl->acl_entry[i].ae_id != ACL_UNDEFINED_ID)
                                return (EINVAL);
                        num_acl_group_obj++;
                        break;
                case ACL_USER:
                        if (acl->acl_entry[i].ae_id == ACL_UNDEFINED_ID)
                                return (EINVAL);
                        num_acl_user++;
                        break;
                case ACL_GROUP:
                        if (acl->acl_entry[i].ae_id == ACL_UNDEFINED_ID)
                                return (EINVAL);
                        num_acl_group++;
                        break;
                case ACL_OTHER:
                        acl->acl_entry[i].ae_id = ACL_UNDEFINED_ID; /* XXX */
                        if (acl->acl_entry[i].ae_id != ACL_UNDEFINED_ID)
                                return (EINVAL);
                        num_acl_other++;
                        break;
                case ACL_MASK:
                        acl->acl_entry[i].ae_id = ACL_UNDEFINED_ID; /* XXX */
                        if (acl->acl_entry[i].ae_id != ACL_UNDEFINED_ID)
                                return (EINVAL);
                        num_acl_mask++;
                        break;
                default:
                        return (EINVAL);
                }
                /*
                 * Check for valid perm entries.
                 */
                if ((acl->acl_entry[i].ae_perm | ACL_PERM_BITS) !=
                    ACL_PERM_BITS)
                        return (EINVAL);
        }
        if ((num_acl_user_obj != 1) || (num_acl_group_obj != 1) ||
            (num_acl_other != 1) || (num_acl_mask != 0 && num_acl_mask != 1))
                return (EINVAL);
        if (((num_acl_group != 0) || (num_acl_user != 0)) &&
            (num_acl_mask != 1))
                return (EINVAL);
        return (0);
}

/*
 * Given a requested mode for a new object, and a default ACL, combine the
 * two to produce a new mode.  Be careful not to clear any bits that aren't
 * intended to be affected by the POSIX.1e ACL.  Eventually, this might also
 * take the cmask as an argument, if we push that down into
 * per-filesystem-code.
 */
mode_t
acl_posix1e_newfilemode(mode_t cmode, struct acl *dacl)
{
        mode_t mode;

        mode = cmode;
        /*
         * The current composition policy is that a permission bit must be
         * set in *both* the ACL and the requested creation mode for it to
         * appear in the resulting mode/ACL.  First clear any possibly
         * effected bits, then reconstruct.
         */
        mode &= ACL_PRESERVE_MASK;
        mode |= (ACL_OVERRIDE_MASK & cmode & acl_posix1e_acl_to_mode(dacl));

        return (mode);
}