source3/smbd/file_access.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    Check access to files based on security descriptors.
   4    Copyright (C) Jeremy Allison 2005-2006.
   5    Copyright (C) Michael Adam 2007.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19 */
  20
  21 #include "includes.h"
  22
  23 #undef  DBGC_CLASS
  24 #define DBGC_CLASS DBGC_ACLS
  25
  26 /**
  27  * Security descriptor / NT Token level access check function.
  28  */
  29 bool can_access_file_acl(struct connection_struct *conn,
  30                                 const char * fname,
  31                                 uint32_t access_mask)
  32 {
  33         NTSTATUS status;
  34         uint32_t access_granted;
  35         struct security_descriptor *secdesc = NULL;
  36
  37         status = SMB_VFS_GET_NT_ACL(conn, fname,
  38                                     (OWNER_SECURITY_INFORMATION |
  39                                      GROUP_SECURITY_INFORMATION |
  40                                      DACL_SECURITY_INFORMATION),
  41                                     &secdesc);
  42         if (!NT_STATUS_IS_OK(status)) {
  43                 DEBUG(5, ("Could not get acl: %s\n", nt_errstr(status)));
  44                 return false;
  45         }
  46
  47         status = se_access_check(secdesc, conn->server_info->ptok,
  48                                  access_mask, &access_granted);
  49         TALLOC_FREE(secdesc);
  50         return NT_STATUS_IS_OK(status);
  51 }
  52
  53 /****************************************************************************
  54  Actually emulate the in-kernel access checking for delete access. We need
  55  this to successfully return ACCESS_DENIED on a file open for delete access.
  56 ****************************************************************************/
  57
  58 bool can_delete_file_in_directory(connection_struct *conn, const char *fname)
  59 {
  60         SMB_STRUCT_STAT sbuf;
  61         TALLOC_CTX *ctx = talloc_tos();
  62         char *dname = NULL;
  63
  64         if (!CAN_WRITE(conn)) {
  65                 return False;
  66         }
  67
  68         /* Get the parent directory permission mask and owners. */
  69         if (!parent_dirname_talloc(ctx,
  70                                 fname,
  71                                 &dname,
  72                                 NULL)) {
  73                 return False;
  74         }
  75         if(SMB_VFS_STAT(conn, dname, &sbuf) != 0) {
  76                 return False;
  77         }
  78
  79         /* fast paths first */
  80
  81         if (!S_ISDIR(sbuf.st_mode)) {
  82                 return False;
  83         }
  84         if (conn->server_info->utok.uid == 0 || conn->admin_user) {
  85                 /* I'm sorry sir, I didn't know you were root... */
  86                 return True;
  87         }
  88
  89 #ifdef S_ISVTX
  90         /* sticky bit means delete only by owner or root. */
  91         if (sbuf.st_mode & S_ISVTX) {
  92                 SMB_STRUCT_STAT sbuf_file;
  93                 if(SMB_VFS_STAT(conn, fname, &sbuf_file) != 0) {
  94                         if (errno == ENOENT) {
  95                                 /* If the file doesn't already exist then
  96                                  * yes we'll be able to delete it. */
  97                                 return True;
  98                         }
  99                         return False;
 100                 }
 101                 /*
 102                  * Patch from SATOH Fumiyasu <fumiyas@miraclelinux.com>
 103                  * for bug #3348. Don't assume owning sticky bit
 104                  * directory means write access allowed.
 105                  */
 106                 if (conn->server_info->utok.uid != sbuf_file.st_uid) {
 107                         return False;
 108                 }
 109         }
 110 #endif
 111
 112         /* now for ACL checks */
 113
 114         /*
 115          * There's two ways to get the permission to delete a file: First by
 116          * having the DELETE bit on the file itself and second if that does
 117          * not help, by the DELETE_CHILD bit on the containing directory.
 118          *
 119          * Here we check the other way round because with just posix
 120          * permissions looking at the file itself will never grant DELETE, so
 121          * by looking at the directory first we save one get_acl call.
 122          */
 123
 124         if (can_access_file_acl(conn, dname, FILE_DELETE_CHILD)) {
 125                 return true;
 126         }
 127
 128         return can_access_file_acl(conn, fname, DELETE_ACCESS);
 129 }
 130
 131 /****************************************************************************
 132  Actually emulate the in-kernel access checking for read/write access. We need
 133  this to successfully check for ability to write for dos filetimes.
 134  Note this doesn't take into account share write permissions.
 135 ****************************************************************************/
 136
 137 bool can_access_file_data(connection_struct *conn, const char *fname, SMB_STRUCT_STAT *psbuf, uint32 access_mask)
 138 {
 139         if (!(access_mask & (FILE_READ_DATA|FILE_WRITE_DATA))) {
 140                 return False;
 141         }
 142         access_mask &= (FILE_READ_DATA|FILE_WRITE_DATA);
 143
 144         /* some fast paths first */
 145
 146         DEBUG(10,("can_access_file_data: requesting 0x%x on file %s\n",
 147                 (unsigned int)access_mask, fname ));
 148
 149         if (conn->server_info->utok.uid == 0 || conn->admin_user) {
 150                 /* I'm sorry sir, I didn't know you were root... */
 151                 return True;
 152         }
 153
 154         if (!VALID_STAT(*psbuf)) {
 155                 /* Get the file permission mask and owners. */
 156                 if(SMB_VFS_STAT(conn, fname, psbuf) != 0) {
 157                         return False;
 158                 }
 159         }
 160
 161         /* Check primary owner access. */
 162         if (conn->server_info->utok.uid == psbuf->st_uid) {
 163                 switch (access_mask) {
 164                         case FILE_READ_DATA:
 165                                 return (psbuf->st_mode & S_IRUSR) ? True : False;
 166
 167                         case FILE_WRITE_DATA:
 168                                 return (psbuf->st_mode & S_IWUSR) ? True : False;
 169
 170                         default: /* FILE_READ_DATA|FILE_WRITE_DATA */
 171
 172                                 if ((psbuf->st_mode & (S_IWUSR|S_IRUSR)) == (S_IWUSR|S_IRUSR)) {
 173                                         return True;
 174                                 } else {
 175                                         return False;
 176                                 }
 177                 }
 178         }
 179
 180         /* now for ACL checks */
 181
 182         return can_access_file_acl(conn, fname, access_mask);
 183 }
 184
 185 /****************************************************************************
 186  Userspace check for write access.
 187  Note this doesn't take into account share write permissions.
 188 ****************************************************************************/
 189
 190 bool can_write_to_file(connection_struct *conn, const char *fname, SMB_STRUCT_STAT *psbuf)
 191 {
 192         return can_access_file_data(conn, fname, psbuf, FILE_WRITE_DATA);
 193 }
 194
 195 /****************************************************************************
 196  Check for an existing default Windows ACL on a directory.
 197 ****************************************************************************/
 198
 199 bool directory_has_default_acl(connection_struct *conn, const char *fname)
 200 {
 201         /* returns talloced off tos. */
 202         struct security_descriptor *secdesc = NULL;
 203         unsigned int i;
 204         NTSTATUS status = SMB_VFS_GET_NT_ACL(conn, fname,
 205                                 DACL_SECURITY_INFORMATION, &secdesc);
 206
 207         if (!NT_STATUS_IS_OK(status) || secdesc == NULL) {
 208                 return false;
 209         }
 210
 211         for (i = 0; i < secdesc->dacl->num_aces; i++) {
 212                 struct security_ace *psa = &secdesc->dacl->aces[i];
 213                 if (psa->flags & (SEC_ACE_FLAG_OBJECT_INHERIT|
 214                                 SEC_ACE_FLAG_CONTAINER_INHERIT)) {
 215                         TALLOC_FREE(secdesc);
 216                         return true;
 217                 }
 218         }
 219         TALLOC_FREE(secdesc);
 220         return false;
 221 }