file_move_safe() PermissionError with SELinux

[bhargu]

PermissionError on upload of large files (large enough to not use the in-memory file class) when SELinux is in enforce mode.

The error happens after the file is copied to the destination folder. As seen in the trace below, when copystat is called from file_move_safe, shutil tries to set attributes with setxattr. But this is failing when SELinux is enabled. I noticed on temporarily disabling SELinux that the files which are successfully uploaded now have a context of 'httpd_tmp_t' as opposed to the context of 'httpd_sys_rw_content_t' which the directory is configured with.

So, when SELinux is enabled, setxattr is failing when the context of the file is 'httpd_sys_rw_content_t'.

Traceback (most recent call last):
  File "/home/portal/venv/lib/python3.6/site-packages/django/core/handlers/exception.py", line 41, in inner
    response = get_response(request)
  File "/home/portal/venv/lib/python3.6/site-packages/django/core/handlers/base.py", line 249, in _legacy_get_response
    response = self._get_response(request)
  File "/home/portal/venv/lib/python3.6/site-packages/django/core/handlers/base.py", line 187, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/home/portal/venv/lib/python3.6/site-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/portal/venv/lib/python3.6/site-packages/django/contrib/auth/decorators.py", line 23, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/home/portal/project/assignments/views/views.py", line 270, in edit_answer
    instance.answerfile_set.create(file=upload, file_type=file)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 653, in create
    return super(RelatedManager, self.db_manager(db)).create(**kwargs)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/query.py", line 394, in create
    obj.save(force_insert=True, using=self.db)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/base.py", line 808, in save
    force_update=force_update, update_fields=update_fields)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/base.py", line 838, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/base.py", line 924, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/base.py", line 963, in _do_insert
    using=using, raw=raw)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/query.py", line 1076, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1111, in execute_sql
    for sql, params in self.as_sql():
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1064, in as_sql
    for obj in self.query.objs
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1064, in <listcomp>
    for obj in self.query.objs
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1063, in <listcomp>
    [self.prepare_value(field, self.pre_save_val(field, obj)) for field in fields]
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1013, in pre_save_val
    return field.pre_save(obj, add=True)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/fields/files.py", line 296, in pre_save
    file.save(file.name, file.file, save=False)
  File "/home/portal/venv/lib/python3.6/site-packages/django/db/models/fields/files.py", line 94, in save
    self.name = self.storage.save(name, content, max_length=self.field.max_length)
  File "/home/portal/venv/lib/python3.6/site-packages/django/core/files/storage.py", line 54, in save
    return self._save(name, content)
  File "/home/portal/venv/lib/python3.6/site-packages/django/core/files/storage.py", line 338, in _save
    file_move_safe(content.temporary_file_path(), full_path)
  File "/home/portal/venv/lib/python3.6/site-packages/django/core/files/move.py", line 76, in file_move_safe
    copystat(old_file_name, new_file_name)
  File "/usr/lib64/python3.6/shutil.py", line 225, in copystat
    _copyxattr(src, dst, follow_symlinks=follow)
  File "/usr/lib64/python3.6/shutil.py", line 165, in _copyxattr
    os.setxattr(dst, name, value, follow_symlinks=follow_symlinks)
PermissionError: [Errno 13] Permission denied: '/home/portal/project/media/submission/8/69_424/10465_fxjc_1_27691_uljy_1_46853.png'

[Tim Graham]

Is that a regression in Django 1.11? If so, it may be caused by f734e2d4b2fc4391a4d097b80357724815c1d414 (#28170 was a similar issue). Can you suggest a fix?

[Phillip Marshall]

I'm also getting error code 13 after doing a large upgrade recently, but am not using SELinux like bhargu. I have a CIFS mount set up in debian, and am using a subclass of FileSystemStorage. Outside of python, the mount is being finicky and throws permission errors when i try and chmod anything in it, but adding removing and editing files works fine. In previous django versions, I believe this kind of behavior was just ignored. However my deployment environment has been upgraded as well, so I'm not 100% sure of this.

Like OP says, this does not happen when the file size is smaller than (DATA|FILE)_UPLOAD_MAX_MEMORY_SIZE (which default to 2.5 megs), and setting those to a higher threshold works around the issue.

I wrote a simple patch below to allow for error 13, and this also remedied the issue for me. I'm not sure if it's a good idea to merge, as code 13 seems to be a general permission error. But it would be nice to be able to override this behaviour myself without having to do such a deep fork.

​https://github.com/agrimgt/django/commit/f9b48086d083b1eee800ea752f2c3fd60a8cc448

[Paolo Donadeo]

I have a question: why the ticket has been closed? I can confirm the issue reported by bhargu still present in Django 2.1.3 and I can confirm that the proposed patch:
​https://github.com/agrimgt/django/commit/f9b48086d083b1eee800ea752f2c3fd60a8cc448
works.

This is a show stopper for us: Django simply don't work on a RHEL7 or CentOS7 with SELinux enabled. To deploy Django 2.x I'm forced to fork.

[Tim Graham]

I closed the issue because there wasn't a response to comment 1.

[Paul Boddie]

One factor that may be involved is the user of the process when a Django application is deployed using mod_wsgi.

I found that using the WSGIDaemonProcess directive with a user other than apache (on Fedora, perhaps www-user on Debian), attempts to upload files failed in the way described, but with the apache user involved (and with appropriate permissions on directories for writing uploaded content) no such error occurred.

It occurs to me that the apache user may be configured in SELinux to not attempt to relabel files in an inappropriate way, or that the apache user is able to preserve httpd_sys_rw_content_t labels whereas other users are not. This is speculation, however, since I have not investigated this in any depth (and the SELinux documentation is often incoherent or opaque).

[Yuri Konotopov]

I created ​PR 16056

[Mariusz Felisiak <felisiak.mariusz@…>]

In 64e5ef1:

Fixed #29027 -- Fixed file_move_safe() crash when moving files with SELinux.

Thanks Florian Apolloner for the review.