source: vendor/3.6.9/source3/smbd/file_access.c

/*
   Unix SMB/CIFS implementation.
   Check access to files based on security descriptors.
   Copyright (C) Jeremy Allison 2005-2006.
   Copyright (C) Michael Adam 2007.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "system/filesys.h"
#include "../libcli/security/security.h"
#include "../librpc/gen_ndr/ndr_security.h"
#include "smbd/smbd.h"

#undef  DBGC_CLASS
#define DBGC_CLASS DBGC_ACLS

/**
 * Security descriptor / NT Token level access check function.
 */
bool can_access_file_acl(struct connection_struct *conn,
                         const struct smb_filename *smb_fname,
                         uint32_t access_mask)
{
        NTSTATUS status;
        uint32_t access_granted;
        struct security_descriptor *secdesc = NULL;
        bool ret;

        if (get_current_uid(conn) == (uid_t)0) {
                /* I'm sorry sir, I didn't know you were root... */
                return true;
        }

        if (access_mask == DELETE_ACCESS &&
                        VALID_STAT(smb_fname->st) &&
                        S_ISLNK(smb_fname->st.st_ex_mode)) {
                /* We can always delete a symlink. */
                return true;
        }

        status = SMB_VFS_GET_NT_ACL(conn, smb_fname->base_name,
                                    (SECINFO_OWNER |
                                     SECINFO_GROUP |
                                     SECINFO_DACL),
                                    &secdesc);
        if (!NT_STATUS_IS_OK(status)) {
                DEBUG(5, ("Could not get acl: %s\n", nt_errstr(status)));
                ret = false;
                goto out;
        }

        status = se_access_check(secdesc, get_current_nttok(conn),
                                 access_mask, &access_granted);
        ret = NT_STATUS_IS_OK(status);

        if (DEBUGLEVEL >= 10) {
                DEBUG(10,("can_access_file_acl for file %s "
                        "access_mask 0x%x, access_granted 0x%x "
                        "access %s\n",
                        smb_fname_str_dbg(smb_fname),
                        (unsigned int)access_mask,
                        (unsigned int)access_granted,
                        ret ? "ALLOWED" : "DENIED" ));
                NDR_PRINT_DEBUG(security_descriptor, secdesc);
        }
 out:
        TALLOC_FREE(secdesc);
        return ret;
}

/****************************************************************************
 Actually emulate the in-kernel access checking for delete access. We need
 this to successfully return ACCESS_DENIED on a file open for delete access.
****************************************************************************/

bool can_delete_file_in_directory(connection_struct *conn,
                                  const struct smb_filename *smb_fname)
{
        TALLOC_CTX *ctx = talloc_tos();
        char *dname = NULL;
        struct smb_filename *smb_fname_parent = NULL;
        NTSTATUS status;
        bool ret;

        if (!CAN_WRITE(conn)) {
                return False;
        }

        if (!lp_acl_check_permissions(SNUM(conn))) {
                /* This option means don't check. */
                return true;
        }

        /* Get the parent directory permission mask and owners. */
        if (!parent_dirname(ctx, smb_fname->base_name, &dname, NULL)) {
                return False;
        }

        status = create_synthetic_smb_fname(ctx, dname, NULL, NULL,
                                            &smb_fname_parent);
        if (!NT_STATUS_IS_OK(status)) {
                ret = false;
                goto out;
        }

        if(SMB_VFS_STAT(conn, smb_fname_parent) != 0) {
                ret = false;
                goto out;
        }

        /* fast paths first */

        if (!S_ISDIR(smb_fname_parent->st.st_ex_mode)) {
                ret = false;
                goto out;
        }
        if (get_current_uid(conn) == (uid_t)0) {
                /* I'm sorry sir, I didn't know you were root... */
                ret = true;
                goto out;
        }

#ifdef S_ISVTX
        /* sticky bit means delete only by owner of file or by root or
         * by owner of directory. */
        if (smb_fname_parent->st.st_ex_mode & S_ISVTX) {
                if (!VALID_STAT(smb_fname->st)) {
                        /* If the file doesn't already exist then
                         * yes we'll be able to delete it. */
                        ret = true;
                        goto out;
                }

                /*
                 * Patch from SATOH Fumiyasu <fumiyas@miraclelinux.com>
                 * for bug #3348. Don't assume owning sticky bit
                 * directory means write access allowed.
                 * Fail to delete if we're not the owner of the file,
                 * or the owner of the directory as we have no possible
                 * chance of deleting. Otherwise, go on and check the ACL.
                 */
                if ((get_current_uid(conn) !=
                        smb_fname_parent->st.st_ex_uid) &&
                    (get_current_uid(conn) != smb_fname->st.st_ex_uid)) {
                        DEBUG(10,("can_delete_file_in_directory: not "
                                  "owner of file %s or directory %s",
                                  smb_fname_str_dbg(smb_fname),
                                  smb_fname_str_dbg(smb_fname_parent)));
                        ret = false;
                        goto out;
                }
        }
#endif

        /* now for ACL checks */

        /*
         * There's two ways to get the permission to delete a file: First by
         * having the DELETE bit on the file itself and second if that does
         * not help, by the DELETE_CHILD bit on the containing directory.
         *
         * Here we only check the directory permissions, we will
         * check the file DELETE permission separately.
         */

        ret = can_access_file_acl(conn, smb_fname_parent, FILE_DELETE_CHILD);
 out:
        TALLOC_FREE(dname);
        TALLOC_FREE(smb_fname_parent);
        return ret;
}

/****************************************************************************
 Actually emulate the in-kernel access checking for read/write access. We need
 this to successfully check for ability to write for dos filetimes.
 Note this doesn't take into account share write permissions.
****************************************************************************/

bool can_access_file_data(connection_struct *conn,
                          const struct smb_filename *smb_fname,
                          uint32 access_mask)
{
        if (!(access_mask & (FILE_READ_DATA|FILE_WRITE_DATA))) {
                return False;
        }
        access_mask &= (FILE_READ_DATA|FILE_WRITE_DATA);

        /* some fast paths first */

        DEBUG(10,("can_access_file_data: requesting 0x%x on file %s\n",
                  (unsigned int)access_mask, smb_fname_str_dbg(smb_fname)));

        if (get_current_uid(conn) == (uid_t)0) {
                /* I'm sorry sir, I didn't know you were root... */
                return True;
        }

        SMB_ASSERT(VALID_STAT(smb_fname->st));

        /* Check primary owner access. */
        if (get_current_uid(conn) == smb_fname->st.st_ex_uid) {
                switch (access_mask) {
                        case FILE_READ_DATA:
                                return (smb_fname->st.st_ex_mode & S_IRUSR) ?
                                    True : False;

                        case FILE_WRITE_DATA:
                                return (smb_fname->st.st_ex_mode & S_IWUSR) ?
                                    True : False;

                        default: /* FILE_READ_DATA|FILE_WRITE_DATA */

                                if ((smb_fname->st.st_ex_mode &
                                        (S_IWUSR|S_IRUSR)) ==
                                    (S_IWUSR|S_IRUSR)) {
                                        return True;
                                } else {
                                        return False;
                                }
                }
        }

        /* now for ACL checks */

        return can_access_file_acl(conn, smb_fname, access_mask);
}

/****************************************************************************
 Userspace check for write access.
 Note this doesn't take into account share write permissions.
****************************************************************************/

bool can_write_to_file(connection_struct *conn,
                       const struct smb_filename *smb_fname)
{
        return can_access_file_data(conn, smb_fname, FILE_WRITE_DATA);
}

/****************************************************************************
 Check for an existing default Windows ACL on a directory.
****************************************************************************/

bool directory_has_default_acl(connection_struct *conn, const char *fname)
{
        /* returns talloced off tos. */
        struct security_descriptor *secdesc = NULL;
        unsigned int i;
        NTSTATUS status = SMB_VFS_GET_NT_ACL(conn, fname,
                                SECINFO_DACL, &secdesc);

        if (!NT_STATUS_IS_OK(status) ||
                        secdesc == NULL ||
                        secdesc->dacl == NULL) {
                TALLOC_FREE(secdesc);
                return false;
        }

        for (i = 0; i < secdesc->dacl->num_aces; i++) {
                struct security_ace *psa = &secdesc->dacl->aces[i];
                if (psa->flags & (SEC_ACE_FLAG_OBJECT_INHERIT|
                                SEC_ACE_FLAG_CONTAINER_INHERIT)) {
                        TALLOC_FREE(secdesc);
                        return true;
                }
        }
        TALLOC_FREE(secdesc);
        return false;
}