source/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         bool result;
  34         NTSTATUS status;
  35         uint32_t access_granted;
  36         struct security_descriptor *secdesc = NULL;
  37
  38         status = SMB_VFS_GET_NT_ACL(conn, fname,
  39                                     (OWNER_SECURITY_INFORMATION |
  40                                      GROUP_SECURITY_INFORMATION |
  41                                      DACL_SECURITY_INFORMATION),
  42                                     &secdesc);
  43         if (!NT_STATUS_IS_OK(status)) {
  44                 DEBUG(5, ("Could not get acl: %s\n", nt_errstr(status)));
  45                 return false;
  46         }
  47
  48         result = se_access_check(secdesc, conn->server_info->ptok,
  49                                  access_mask, &access_granted, &status);
  50         TALLOC_FREE(secdesc);
  51         return result;
  52 }
  53
  54 /****************************************************************************
  55  Actually emulate the in-kernel access checking for delete access. We need
  56  this to successfully return ACCESS_DENIED on a file open for delete access.
  57 ****************************************************************************/
  58
  59 bool can_delete_file_in_directory(connection_struct *conn, const char *fname)
  60 {
  61         SMB_STRUCT_STAT sbuf;
  62         TALLOC_CTX *ctx = talloc_tos();
  63         char *dname = NULL;
  64
  65         if (!CAN_WRITE(conn)) {
  66                 return False;
  67         }
  68
  69         /* Get the parent directory permission mask and owners. */
  70         if (!parent_dirname_talloc(ctx,
  71                                 fname,
  72                                 &dname,
  73                                 NULL)) {
  74                 return False;
  75         }
  76         if(SMB_VFS_STAT(conn, dname, &sbuf) != 0) {
  77                 return False;
  78         }
  79
  80         /* fast paths first */
  81
  82         if (!S_ISDIR(sbuf.st_mode)) {
  83                 return False;
  84         }
  85         if (conn->server_info->utok.uid == 0 || conn->admin_user) {
  86                 /* I'm sorry sir, I didn't know you were root... */
  87                 return True;
  88         }
  89
  90 #ifdef S_ISVTX
  91         /* sticky bit means delete only by owner or root. */
  92         if (sbuf.st_mode & S_ISVTX) {
  93                 SMB_STRUCT_STAT sbuf_file;
  94                 if(SMB_VFS_STAT(conn, fname, &sbuf_file) != 0) {
  95                         if (errno == ENOENT) {
  96                                 /* If the file doesn't already exist then
  97                                  * yes we'll be able to delete it. */
  98                                 return True;
  99                         }
 100                         return False;
 101                 }
 102                 /*
 103                  * Patch from SATOH Fumiyasu <fumiyas@miraclelinux.com>
 104                  * for bug #3348. Don't assume owning sticky bit
 105                  * directory means write access allowed.
 106                  */
 107                 if (conn->server_info->utok.uid != sbuf_file.st_uid) {
 108                         return False;
 109                 }
 110         }
 111 #endif
 112
 113         /* now for ACL checks */
 114
 115         /*
 116          * There's two ways to get the permission to delete a file: First by
 117          * having the DELETE bit on the file itself and second if that does
 118          * not help, by the DELETE_CHILD bit on the containing directory.
 119          *
 120          * Here we check the other way round because with just posix
 121          * permissions looking at the file itself will never grant DELETE, so
 122          * by looking at the directory first we save one get_acl call.
 123          */
 124
 125         if (can_access_file_acl(conn, dname, FILE_DELETE_CHILD)) {
 126                 return true;
 127         }
 128
 129         return can_access_file_acl(conn, fname, DELETE_ACCESS);
 130 }
 131
 132 /****************************************************************************
 133  Actually emulate the in-kernel access checking for read/write access. We need
 134  this to successfully check for ability to write for dos filetimes.
 135  Note this doesn't take into account share write permissions.
 136 ****************************************************************************/
 137
 138 bool can_access_file_data(connection_struct *conn, const char *fname, SMB_STRUCT_STAT *psbuf, uint32 access_mask)
 139 {
 140         if (!(access_mask & (FILE_READ_DATA|FILE_WRITE_DATA))) {
 141                 return False;
 142         }
 143         access_mask &= (FILE_READ_DATA|FILE_WRITE_DATA);
 144
 145         /* some fast paths first */
 146
 147         DEBUG(10,("can_access_file_data: requesting 0x%x on file %s\n",
 148                 (unsigned int)access_mask, fname ));
 149
 150         if (conn->server_info->utok.uid == 0 || conn->admin_user) {
 151                 /* I'm sorry sir, I didn't know you were root... */
 152                 return True;
 153         }
 154
 155         if (!VALID_STAT(*psbuf)) {
 156                 /* Get the file permission mask and owners. */
 157                 if(SMB_VFS_STAT(conn, fname, psbuf) != 0) {
 158                         return False;
 159                 }
 160         }
 161
 162         /* Check primary owner access. */
 163         if (conn->server_info->utok.uid == psbuf->st_uid) {
 164                 switch (access_mask) {
 165                         case FILE_READ_DATA:
 166                                 return (psbuf->st_mode & S_IRUSR) ? True : False;
 167
 168                         case FILE_WRITE_DATA:
 169                                 return (psbuf->st_mode & S_IWUSR) ? True : False;
 170
 171                         default: /* FILE_READ_DATA|FILE_WRITE_DATA */
 172
 173                                 if ((psbuf->st_mode & (S_IWUSR|S_IRUSR)) == (S_IWUSR|S_IRUSR)) {
 174                                         return True;
 175                                 } else {
 176                                         return False;
 177                                 }
 178                 }
 179         }
 180
 181         /* now for ACL checks */
 182
 183         return can_access_file_acl(conn, fname, access_mask);
 184 }
 185
 186 /****************************************************************************
 187  Userspace check for write access.
 188  Note this doesn't take into account share write permissions.
 189 ****************************************************************************/
 190
 191 bool can_write_to_file(connection_struct *conn, const char *fname, SMB_STRUCT_STAT *psbuf)
 192 {
 193         return can_access_file_data(conn, fname, psbuf, FILE_WRITE_DATA);
 194 }
 195
 196 /****************************************************************************
 197  Check for an existing default Windows ACL on a directory.
 198 ****************************************************************************/
 199
 200 bool directory_has_default_acl(connection_struct *conn, const char *fname)
 201 {
 202         /* returns talloced off tos. */
 203         struct security_descriptor *secdesc = NULL;
 204         unsigned int i;
 205         NTSTATUS status = SMB_VFS_GET_NT_ACL(conn, fname,
 206                                 DACL_SECURITY_INFORMATION, &secdesc);
 207
 208         if (!NT_STATUS_IS_OK(status) || secdesc == NULL) {
 209                 return false;
 210         }
 211
 212         for (i = 0; i < secdesc->dacl->num_aces; i++) {
 213                 struct security_ace *psa = &secdesc->dacl->aces[i];
 214                 if (psa->flags & (SEC_ACE_FLAG_OBJECT_INHERIT|
 215                                 SEC_ACE_FLAG_CONTAINER_INHERIT)) {
 216                         TALLOC_FREE(secdesc);
 217                         return true;
 218                 }
 219         }
 220         TALLOC_FREE(secdesc);
 221         return false;
 222 }