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 #include "system/filesys.h"
  23 #include "../libcli/security/security.h"
  24 #include "../librpc/gen_ndr/ndr_security.h"
  25 #include "smbd/smbd.h"
  26
  27 #undef  DBGC_CLASS
  28 #define DBGC_CLASS DBGC_ACLS
  29
  30 /**
  31  * Security descriptor / NT Token level access check function.
  32  */
  33 bool can_access_file_acl(struct connection_struct *conn,
  34                          const struct smb_filename *smb_fname,
  35                          uint32_t access_mask)
  36 {
  37         NTSTATUS status;
  38         uint32_t access_granted;
  39         struct security_descriptor *secdesc = NULL;
  40         bool ret;
  41
  42         if (get_current_uid(conn) == (uid_t)0) {
  43                 /* I'm sorry sir, I didn't know you were root... */
  44                 return true;
  45         }
  46
  47         if (access_mask == DELETE_ACCESS &&
  48                         VALID_STAT(smb_fname->st) &&
  49                         S_ISLNK(smb_fname->st.st_ex_mode)) {
  50                 /* We can always delete a symlink. */
  51                 return true;
  52         }
  53
  54         status = SMB_VFS_GET_NT_ACL(conn, smb_fname->base_name,
  55                                     (SECINFO_OWNER |
  56                                      SECINFO_GROUP |
  57                                      SECINFO_DACL),
  58                                     &secdesc);
  59         if (!NT_STATUS_IS_OK(status)) {
  60                 DEBUG(5, ("Could not get acl: %s\n", nt_errstr(status)));
  61                 ret = false;
  62                 goto out;
  63         }
  64
  65         status = se_access_check(secdesc, get_current_nttok(conn),
  66                                  access_mask, &access_granted);
  67         ret = NT_STATUS_IS_OK(status);
  68
  69         if (DEBUGLEVEL >= 10) {
  70                 DEBUG(10,("can_access_file_acl for file %s "
  71                         "access_mask 0x%x, access_granted 0x%x "
  72                         "access %s\n",
  73                         smb_fname_str_dbg(smb_fname),
  74                         (unsigned int)access_mask,
  75                         (unsigned int)access_granted,
  76                         ret ? "ALLOWED" : "DENIED" ));
  77                 NDR_PRINT_DEBUG(security_descriptor, secdesc);
  78         }
  79  out:
  80         TALLOC_FREE(secdesc);
  81         return ret;
  82 }
  83
  84 /****************************************************************************
  85  Actually emulate the in-kernel access checking for delete access. We need
  86  this to successfully return ACCESS_DENIED on a file open for delete access.
  87 ****************************************************************************/
  88
  89 bool can_delete_file_in_directory(connection_struct *conn,
  90                                   const struct smb_filename *smb_fname)
  91 {
  92         TALLOC_CTX *ctx = talloc_tos();
  93         char *dname = NULL;
  94         struct smb_filename *smb_fname_parent = NULL;
  95         NTSTATUS status;
  96         bool ret;
  97
  98         if (!CAN_WRITE(conn)) {
  99                 return False;
 100         }
 101
 102         if (!lp_acl_check_permissions(SNUM(conn))) {
 103                 /* This option means don't check. */
 104                 return true;
 105         }
 106
 107         /* Get the parent directory permission mask and owners. */
 108         if (!parent_dirname(ctx, smb_fname->base_name, &dname, NULL)) {
 109                 return False;
 110         }
 111
 112         status = create_synthetic_smb_fname(ctx, dname, NULL, NULL,
 113                                             &smb_fname_parent);
 114         if (!NT_STATUS_IS_OK(status)) {
 115                 ret = false;
 116                 goto out;
 117         }
 118
 119         if(SMB_VFS_STAT(conn, smb_fname_parent) != 0) {
 120                 ret = false;
 121                 goto out;
 122         }
 123
 124         /* fast paths first */
 125
 126         if (!S_ISDIR(smb_fname_parent->st.st_ex_mode)) {
 127                 ret = false;
 128                 goto out;
 129         }
 130         if (get_current_uid(conn) == (uid_t)0) {
 131                 /* I'm sorry sir, I didn't know you were root... */
 132                 ret = true;
 133                 goto out;
 134         }
 135
 136 #ifdef S_ISVTX
 137         /* sticky bit means delete only by owner of file or by root or
 138          * by owner of directory. */
 139         if (smb_fname_parent->st.st_ex_mode & S_ISVTX) {
 140                 if (!VALID_STAT(smb_fname->st)) {
 141                         /* If the file doesn't already exist then
 142                          * yes we'll be able to delete it. */
 143                         ret = true;
 144                         goto out;
 145                 }
 146
 147                 /*
 148                  * Patch from SATOH Fumiyasu <fumiyas@miraclelinux.com>
 149                  * for bug #3348. Don't assume owning sticky bit
 150                  * directory means write access allowed.
 151                  * Fail to delete if we're not the owner of the file,
 152                  * or the owner of the directory as we have no possible
 153                  * chance of deleting. Otherwise, go on and check the ACL.
 154                  */
 155                 if ((get_current_uid(conn) !=
 156                         smb_fname_parent->st.st_ex_uid) &&
 157                     (get_current_uid(conn) != smb_fname->st.st_ex_uid)) {
 158                         DEBUG(10,("can_delete_file_in_directory: not "
 159                                   "owner of file %s or directory %s",
 160                                   smb_fname_str_dbg(smb_fname),
 161                                   smb_fname_str_dbg(smb_fname_parent)));
 162                         ret = false;
 163                         goto out;
 164                 }
 165         }
 166 #endif
 167
 168         /* now for ACL checks */
 169
 170         /*
 171          * There's two ways to get the permission to delete a file: First by
 172          * having the DELETE bit on the file itself and second if that does
 173          * not help, by the DELETE_CHILD bit on the containing directory.
 174          *
 175          * Here we only check the directory permissions, we will
 176          * check the file DELETE permission separately.
 177          */
 178
 179         ret = can_access_file_acl(conn, smb_fname_parent, FILE_DELETE_CHILD);
 180  out:
 181         TALLOC_FREE(dname);
 182         TALLOC_FREE(smb_fname_parent);
 183         return ret;
 184 }
 185
 186 /****************************************************************************
 187  Actually emulate the in-kernel access checking for read/write access. We need
 188  this to successfully check for ability to write for dos filetimes.
 189  Note this doesn't take into account share write permissions.
 190 ****************************************************************************/
 191
 192 bool can_access_file_data(connection_struct *conn,
 193                           const struct smb_filename *smb_fname,
 194                           uint32 access_mask)
 195 {
 196         if (!(access_mask & (FILE_READ_DATA|FILE_WRITE_DATA))) {
 197                 return False;
 198         }
 199         access_mask &= (FILE_READ_DATA|FILE_WRITE_DATA);
 200
 201         /* some fast paths first */
 202
 203         DEBUG(10,("can_access_file_data: requesting 0x%x on file %s\n",
 204                   (unsigned int)access_mask, smb_fname_str_dbg(smb_fname)));
 205
 206         if (get_current_uid(conn) == (uid_t)0) {
 207                 /* I'm sorry sir, I didn't know you were root... */
 208                 return True;
 209         }
 210
 211         SMB_ASSERT(VALID_STAT(smb_fname->st));
 212
 213         /* Check primary owner access. */
 214         if (get_current_uid(conn) == smb_fname->st.st_ex_uid) {
 215                 switch (access_mask) {
 216                         case FILE_READ_DATA:
 217                                 return (smb_fname->st.st_ex_mode & S_IRUSR) ?
 218                                     True : False;
 219
 220                         case FILE_WRITE_DATA:
 221                                 return (smb_fname->st.st_ex_mode & S_IWUSR) ?
 222                                     True : False;
 223
 224                         default: /* FILE_READ_DATA|FILE_WRITE_DATA */
 225
 226                                 if ((smb_fname->st.st_ex_mode &
 227                                         (S_IWUSR|S_IRUSR)) ==
 228                                     (S_IWUSR|S_IRUSR)) {
 229                                         return True;
 230                                 } else {
 231                                         return False;
 232                                 }
 233                 }
 234         }
 235
 236         /* now for ACL checks */
 237
 238         return can_access_file_acl(conn, smb_fname, access_mask);
 239 }
 240
 241 /****************************************************************************
 242  Userspace check for write access.
 243  Note this doesn't take into account share write permissions.
 244 ****************************************************************************/
 245
 246 bool can_write_to_file(connection_struct *conn,
 247                        const struct smb_filename *smb_fname)
 248 {
 249         return can_access_file_data(conn, smb_fname, FILE_WRITE_DATA);
 250 }
 251
 252 /****************************************************************************
 253  Check for an existing default Windows ACL on a directory.
 254 ****************************************************************************/
 255
 256 bool directory_has_default_acl(connection_struct *conn, const char *fname)
 257 {
 258         /* returns talloced off tos. */
 259         struct security_descriptor *secdesc = NULL;
 260         unsigned int i;
 261         NTSTATUS status = SMB_VFS_GET_NT_ACL(conn, fname,
 262                                 SECINFO_DACL, &secdesc);
 263
 264         if (!NT_STATUS_IS_OK(status) ||
 265                         secdesc == NULL ||
 266                         secdesc->dacl == NULL) {
 267                 TALLOC_FREE(secdesc);
 268                 return false;
 269         }
 270
 271         for (i = 0; i < secdesc->dacl->num_aces; i++) {
 272                 struct security_ace *psa = &secdesc->dacl->aces[i];
 273                 if (psa->flags & (SEC_ACE_FLAG_OBJECT_INHERIT|
 274                                 SEC_ACE_FLAG_CONTAINER_INHERIT)) {
 275                         TALLOC_FREE(secdesc);
 276                         return true;
 277                 }
 278         }
 279         TALLOC_FREE(secdesc);
 280         return false;
 281 }