The current code has a risk of race-conditions, since we pass a path
containing "/" to Fchownat. We could fix this by opening a file descriptor,
however, this does not seem worth the effort. We also don't chown *.name files.
Make sure that the directory belongs to the correct owner before users
can access it. For directories with SUID/SGID mode, there is a risk of
race-conditions when files are created before the correct owner is set.
They will then inherit the wrong user and/or group.
See https://github.com/rfjakob/gocryptfs/issues/327 for more details.
Reported by @slackner at https://github.com/rfjakob/gocryptfs/issues/327 :
Possible race-conditions between file creation and Fchownat
* Assume a system contains a gocryptfs mount as root user
with -allow_other
* As a regular user create a new file with mode containing
the SUID flag and write access for other users
* Before gocryptfs executes the Fchownat call, try to open
the file again, write some exploit code to it, and try to run it.
For a short time, the file is owned by root and has the SUID flag, so
this is pretty dangerous.
The files are apparently processed in alphabetic order, so cli_args.go is
processed before main.go. In order to run before the go-fuse imports, put
the 'ensure fds' code in a separate package. Debug messages are omitted
to avoid additional imports (that might contain other code messing up our
file descriptors).
Setting/removing extended attributes on directories was partially fixed with
commit eff35e60b6. However, on most file systems
it is also possible to do these operations without read access (see tests).
Since we cannot open a write-access fd to a directory, we have to use the
/proc/self/fd trick (already used for ListXAttr) for the other operations aswell.
For simplicity, let's separate the Linux and Darwin code again (basically revert
commit f320b76fd1), and always use the
/proc/self/fd trick on Linux. On Darwin we use the best-effort approach with
openBackingFile() as a fallback.
More discussion about the available options is available in
https://github.com/rfjakob/gocryptfs/issues/308.
Otherwise this can happen, as triggered by xfstests generic/011:
go-fuse: can't convert error type: openat failed: too many open files
The app then gets a misleading "Function not implemented" error.
We alread have this warning in Open(), but xfstests generic/488
causes "too many open files" via Create. Add the same message so
the user sees what is going on.
Go version go1.10.7 linux/amd64 complains with:
internal/fusefrontend_reverse/rfs.go:333: declaration of "entries" shadows
declaration at internal/fusefrontend_reverse/rfs.go:327
Fixes https://github.com/rfjakob/gocryptfs/issues/286 :
While the actual file is properly excluded, the * .name file is still leaked in the directory listing:
```
drwxr-xr-x 2 sebastian sebastian 4,0K Dez 17 14:58 .
drwxr-xr-x 7 sebastian sebastian 4,0K Dez 17 14:45 ..
-r-------- 1 sebastian sebastian 408 Dez 17 14:56 gocryptfs.conf
-r--r--r-- 1 sebastian sebastian 16 Dez 17 14:58 gocryptfs.diriv
-r--r--r-- 1 sebastian sebastian 320 Dez 17 14:58 gocryptfs.longname.3vZ_r3eDPb1_fL3j5VA4rd_bcKWLKT9eaxOVIGK5HFA.name
```
Excluded files showed up in directory listing like this:
drwxr-xr-x 2 sebastian sebastian 4,0K Dez 17 14:48 .
drwxr-xr-x 7 sebastian sebastian 4,0K Dez 17 14:45 ..
-????????? ? ? ? ? ? abcd
-r-------- 1 sebastian sebastian 366 Dez 17 14:45 gocryptfs.conf
Fixes https://github.com/rfjakob/gocryptfs/issues/285
When the old size is zero, there are no existing blocks to merge the
new data with. Directly use Ftruncate if the size is block-aligned.
Fixes https://github.com/rfjakob/gocryptfs/issues/305
Bug looked like this:
$ ls -l .
total 0
drwxrwxr-x. 2 jakob jakob 60 Jan 3 15:42 foo
-rw-rw-r--. 1 jakob jakob 0 Jan 3 15:46 x
$ ls -l .
ls: cannot access '.': No such file or directory
(only happened when "" was in the dirCache)
This function is in all fastpaths, will get a cache, and needs
its own file.
renamed: internal/fusefrontend/names.go -> internal/fusefrontend/openbackingdir.go
renamed: internal/fusefrontend/names_test.go -> internal/fusefrontend/openbackingdir_test.go
Sebastian Lackner