Unfortunately, faccessat in Linux ignores AT_SYMLINK_NOFOLLOW,
so this is not completely atomic.
Given that the information you get from access is not very
interesting, it seems good enough.
https://github.com/rfjakob/gocryptfs/issues/165
Add faccessat(2) with a hack for symlink, because the
kernel does not actually looks at the passed flags.
From man 2 faccessat:
C library/kernel differences
The raw faccessat() system call takes only the first three argu‐
ments. The AT_EACCESS and AT_SYMLINK_NOFOLLOW flags are actually
implemented within the glibc wrapper function for faccessat().
...when opening intermedia directories to give us an
extra layer of safety.
From the FreeBSD man page:
This flag can be used to prevent applications with elevated
privileges from opening files which are even unsafe to open with O_RDONLY,
such as device nodes.
...by using the new OpenNofollow helper.
The benchmark shows a small but acceptable performance loss:
$ ./benchmark-reverse.bash
LS: 2.182
CAT: 18.221
Tracking ticket: https://github.com/rfjakob/gocryptfs/issues/165
Now that we have Fstatat we can use it in Getdents to
get rid of the path name.
Also, add an emulated version of getdents for MacOS. This allows
to drop the !HaveGetdents special cases from fusefrontend.
Modify the getdents test to test both native getdents and the emulated
version.
In PlaintextNames mode the "gocryptfs.longname." prefix does not have any
special meaning. We should not attempt to delete any .name files.
Partially fixes https://github.com/rfjakob/gocryptfs/issues/174
This is already done in regular mode, but was missing when PlaintextNames mode
is enabled. As a result, symlinks created by non-root users were still owned
by root afterwards.
Fixes https://github.com/rfjakob/gocryptfs/issues/176
In PlaintextNames mode the "gocryptfs.longname." prefix does not have any
special meaning. We should not attempt to read the directory IV or to
create special .name files.
Partially fixes https://github.com/rfjakob/gocryptfs/issues/174
If the user manages to replace the directory with
a symlink at just the right time, we could be tricked
into chown'ing the wrong file.
This change fixes the race by using fchownat, which
unfortunately is not available on darwin, hence a compat
wrapper is added.
Scenario, as described by @slackner at
https://github.com/rfjakob/gocryptfs/issues/177 :
1. Create a forward mount point with `plaintextnames` enabled
2. Mount as root user with `allow_other`
3. For testing purposes create a file `/tmp/file_owned_by_root`
which is owned by the root user
4. As a regular user run inside of the GoCryptFS mount:
```
mkdir tempdir
mknod tempdir/file_owned_by_root p &
mv tempdir tempdir2
ln -s /tmp tempdir
```
When the steps are done fast enough and in the right order
(run in a loop!), the device file will be created in
`tempdir`, but the `lchown` will be executed by following
the symlink. As a result, the ownership of the file located
at `/tmp/file_owned_by_root` will be changed.
If the symlink target gets too long due to base64 encoding, we should
return ENAMETOOLONG instead of having the kernel reject the data and
returning an I/O error to the user.
Fixes https://github.com/rfjakob/gocryptfs/issues/167
Fixes https://github.com/rfjakob/gocryptfs/issues/168
Steps to reproduce the problem:
* Create a regular reverse mount point
* Create files with the same very long name in multiple directories - so far
everything works as expected, and it will appear with a different name each
time, for example, gocryptfs.longname.A in directory A and
gocryptfs.longname.B in directory B
* Try to access a path with A/gocryptfs.longname.B or B/gocryptfs.longname.A -
this should fail, but it actually works.
The problem is that the longname cache only uses the path as key and not the
dir or divIV. Assume an attacker can directly interact with a reverse mount and
knows the relation longname path -> unencoded path in one directory, it allows
to test if the same unencoded filename appears in any other directory.
Fixes https://github.com/rfjakob/gocryptfs/issues/171
Steps to reproduce:
* Create a regular forward mount point
* Create a new directory in the mount point
* Manually delete the gocryptfs.diriv file from the corresponding ciphertext
directory
* Attempt to delete the directory with 'rmdir <dirname>'
Although the code explicitly checks for empty directories, it will still attempt
to move the non-existent gocryptfs.diriv file and fails with:
rmdir: failed to remove '<dirname>': No such file or directory
Fixes https://github.com/rfjakob/gocryptfs/issues/170
Steps to reproduce the problem:
* Create a regular forward mount point
* Create a file with a shortname and one with a long filename
* Try to run 'mv <shortname> <longname>'
This should actually work and replace the existing file, but instead it
fails with:
mv: cannot move '<shortname>' to '<longname>': File exists
The problem is the creation of the .name file. If the target already exists
we can safely ignore the EEXIST error and just keep the existing .name file.
Allows to use /dev/random for generating the master key instead of the
default Go implementation. When the kernel random generator has been
properly initialized both are considered equally secure, however:
* Versions of Go prior to 1.9 just fall back to /dev/urandom if the
getrandom() syscall would be blocking (Go Bug #19274)
* Kernel versions prior to 3.17 do not support getrandom(), and there
is no check if the random generator has been properly initialized
before reading from /dev/urandom
This is especially useful for embedded hardware with low-entroy. Please
note that generation of the master key might block indefinitely if the
kernel cannot harvest enough entropy.
At the moment, it does two things:
1. Disable stat() caching so changes to the backing storage show up
immediately.
2. Disable hard link tracking, as the inode numbers on the backing
storage are not stable when files are deleted and re-created behind
our back. This would otherwise produce strange "file does not exist"
and other errors.
Mitigates https://github.com/rfjakob/gocryptfs/issues/156
