If the connection provided to sftp.NewServer is closed,
Serve returns the io.EOF error verbatim from io.Reader.Read.
This is an odd error since this is an expected situation,
so we manually ignore io.EOF.
This is somewhat buggy since the sftp package itself
incorrectly reports io.EOF in cases where it should actually
be reporting io.ErrUnexpectedEOF.
See https://github.com/pkg/sftp/pull/554 which patches Serve to
return nil on clean closes and fixes buggy uses of io.ReadFull.
Fixes#8592
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
There are two race conditions in output handling.
The first race condition is due to a misuse of exec.Cmd.StdoutPipe.
The documentation explicitly forbids concurrent use of StdoutPipe
with exec.Cmd.Wait (see golang/go#60908) because Wait will
close both sides of the pipe once the process ends without
any guarantees that all data has been read from the pipe.
To fix this, we allocate the os.Pipes ourselves and
manage cleanup ourselves when the process has ended.
The second race condition is because sshSession.run waits
upon exec.Cmd to finish and then immediately proceeds to call ss.Exit,
which will close all output streams going to the SSH client.
This may interrupt any asynchronous io.Copy still copying data.
To fix this, we close the write-side of the os.Pipes after
the process has finished (and before calling ss.Exit) and
synchronously wait for the io.Copy routines to finish.
Fixes#7601
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Co-authored-by: Maisem Ali <maisem@tailscale.com>
On redhat 9 and similarly locked down systems, root user does not have
access to a users directory. This fix does not set a directory for the
incubator process and instead sets the directory when the actual process
requested by remote user is executed.
Fixes#8118
Signed-off-by: Derek Burdick <derek-burdick@users.noreply.github.com>
Trying to SSH when SELinux is enforced results in errors like:
```
➜ ~ ssh ec2-user@<ip>
Last login: Thu Jun 1 22:51:44 from <ip2>
ec2-user: no shell: Permission denied
Connection to <ip> closed.
```
while the `/var/log/audit/audit.log` has
```
type=AVC msg=audit(1685661291.067:465): avc: denied { transition } for pid=5296 comm="login" path="/usr/bin/bash" dev="nvme0n1p1" ino=2564 scontext=system_u:system_r:unconfined_service_t:s0 tcontext=unconfined_u:unconfined_r:unconfined_t:s0 tclass=process permissive=0
```
The right fix here would be to somehow install the appropriate context when
tailscale is installed on host, but until we figure out a way to do that
stop using the `login` cmd in these situations.
Updates #4908
Signed-off-by: Maisem Ali <maisem@tailscale.com>
This basically allows running services on the SSH client and reaching
them from the SSH server during the session.
Updates #6575
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Max username length is increased to 256 on linux to match /usr/include/bits/local_lim.h
Fixes#8277
Signed-off-by: Derek Burdick <derek-burdick@users.noreply.github.com>
This change introduces a SSHSessionRecordingFailed event type
that is used when a session recording fails to start or fails during a
session, and the on failure indicates that it should fail open.
Updates tailscale/corp#9967
Signed-off-by: Charlotte Brandhorst-Satzkorn <charlotte@tailscale.com>
58ab66ec51 added LDAP support
for #4945 by shelling out to getdent.
It was supposed to fall back to the old method when getdent wasn't
found, but some variable name confusion (uid vs username) meant the
old path wasn't calling the right lookup function (user.LookupId
instead of user.Lookup).
Which meant that changed probably also broke FreeBSD and macOS SSH
support in addition to the reported OpenWRT regression.
The gokrazy support didn't look right either.
Fixes#8180
Change-Id: I273bbe96fe98b2517fbf0335fd476b483c051554
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We were only closing on side of the pty/tty pair.
Close the other side too.
Thanks to @fritterhoff for reporting and debugging the issue!
Fixes#8119
Signed-off-by: Maisem Ali <maisem@tailscale.com>
The previous commit 58ab66e added ssh/tailssh/user.go as part of
working on #4945. So move some more user-related code over to it.
Updates #cleanup
Change-Id: I24de66df25ffb8f867e1a0a540d410f9ef16d7b0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This change adds a ConnectionID field to both SSHEventNotifyRequest and
CastHeader that identifies the ID of a connection to the SSH server.
Updates tailscale/corp#9967
Signed-off-by: Charlotte Brandhorst-Satzkorn <charlotte@tailscale.com>
This change sends an SSHEventNotificationRequest over noise when a
SSH session is set to fail closed and the session is unable to start
because a recorder is not available or a session is terminated because
connection to the recorder is ended. Each of these scenarios have their
own event type.
Updates tailscale/corp#9967
Signed-off-by: Charlotte Brandhorst-Satzkorn <charlotte@tailscale.com>
This is part of an effort to clean up tailscaled initialization between
tailscaled, tailscaled Windows service, tsnet, and the mac GUI.
Updates #8036
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We removed it earlier in 916aa782af, but we still want to support it for some time longer.
Updates tailscale/corp#9967
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Previously we would error out when the recording server disappeared after the in memory
buffer filled up for the io.Copy. This makes it so that we handle failing open correctly
in that path.
Updates tailscale/corp#9967
Signed-off-by: Maisem Ali <maisem@tailscale.com>
This adds support to try dialing out to multiple recorders each
with a 5s timeout and an overall 30s timeout. It also starts respecting
the actions `OnRecordingFailure` field if set, if it is not set
it fails open.
Updates tailscale/corp#9967
Signed-off-by: Maisem Ali <maisem@tailscale.com>
This adds an initial and intentionally minimal configuration for
golang-ci, fixes the issues reported, and adds a GitHub Action to check
new pull requests against this linter configuration.
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I8f38fbc315836a19a094d0d3e986758b9313f163
There were two code paths that could fail depending on how fast
the recorder responses. This fixes that by returning the correct
error from both paths.
Fixes#7707
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Previously it would dial out using the http.DefaultClient, however that doesn't work
when tailscaled is running in userspace mode (e.g. when testing).
Updates tailscale/corp#9967
Signed-off-by: Maisem Ali <maisem@tailscale.com>
This change focuses on the backend log ID, which is the mostly commonly
used in the client. Tests which don't seem to make use of the log ID
just use the zero value.
Signed-off-by: Will Norris <will@tailscale.com>
Move the assertions about our post-privilege-drop UID/GID out of the
conditional if statement and always run them; I haven't been able to
find a case where this would fail. Defensively add an envknob to disable
this feature, however, which we can remove after the 1.40 release.
Updates #7616
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Iaec3dba9248131920204bd6c6d34bbc57a148185
This makes it less likely that we trip over bugs like golang/go#1435.
Updates #7616
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Ic28c03c3ad8ed5274a795c766b767fa876029f0e
Otherwise we see errors like
```
ssh-session(sess-20230322T005655-5562985593): recording: error sending recording to <addr>:80: Post "http://<addr>:80/record": context canceled
```
The ss.ctx is closed when the session closes, but we don't want to break the upload at that time. Instead we want to wait for the session to
close the writer when it finishes, which it is already doing.
Updates tailscale/corp#9967
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Currently we only send down recorders in first action, allow the final action
to replace them but not to drop them.
Updates tailscale/corp#9967
Signed-off-by: Maisem Ali <maisem@tailscale.com>
On FreeBSD and Darwin, changing a process's supplementary groups with
setgroups(2) will also change the egid of the process, setting it to the
first entry in the provided list. This is distinct from the behaviour on
other platforms (and possibly a violation of the POSIX standard).
Because of this, on FreeBSD with no TTY, our incubator code would
previously not change the process's gid, because it would read the
newly-changed egid, compare it against the expected egid, and since they
matched, not change the gid. Because we didn't use the 'login' program
on FreeBSD without a TTY, this would propagate to a child process.
This could be observed by running "id -p" in two contexts. The expected
output, and the output returned when running from a SSH shell, is:
andrew@freebsd:~ $ id -p
uid andrew
groups andrew
However, when run via "ssh andrew@freebsd id -p", the output would be:
$ ssh andrew@freebsd id -p
login root
uid andrew
rgid wheel
groups andrew
(this could also be observed via "id -g -r" to print just the gid)
We fix this by pulling the details of privilege dropping out into their
own function and prepending the expected gid to the start of the list on
Darwin and FreeBSD.
Finally, we add some tests that run a child process, drop privileges,
and assert that the final UID/GID/additional groups are what we expect.
More information can be found in the following article:
https://www.usenix.org/system/files/login/articles/325-tsafrir.pdf
Updates #7616
Alternative to #7609
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I0e6513c31b121108b50fe561c89e5816d84a45b9
This updates all source files to use a new standard header for copyright
and license declaration. Notably, copyright no longer includes a date,
and we now use the standard SPDX-License-Identifier header.
This commit was done almost entirely mechanically with perl, and then
some minimal manual fixes.
Updates #6865
Signed-off-by: Will Norris <will@tailscale.com>
