User can't use SFTP after chroot

[Bostjan Skufca]

Do you chroot to a directory which is writtable by non-root? Or any of it's
parents all the way up to the root (/)? If so, chroot (and connection) will
fail.

b.



On 1 October 2012 00:30, Jeroen Beckers <dauntless at dauntless.be> wrote:

> Hi,
>
> I've posted this question on ServerFault, but no answer has been found
> (http://serverfault.com/questions/431329/user-cant-sftp-after-chroot).
> I have version 1:5.3p1-3ubuntu7
>
> To sum up: I want to chroot the user sam. Things I have done:
> - add user 'sam' to group 'users'
> - added Subsystem sftp internal-sftp to /etc/ssh/sshd_config (at the
> bottom)
> - added a Match :
>
> --
> Match group users
>     ChrootDirectory %h
>     ForceCommand internal-sftp
>     AllowTcpForwarding no
> --
>
> - changed permission of /home to be owned by root:root and not
> writable by anyone else
> - restarted ssh
>
> When I try to sftp with sam, I get this:
> --
> $ sftp sam at localhost
> Connecting to localhost...
> sam at localhost's password:
> Couldn't read packet: Connection reset by peer
> --
>
> If I remove sam from the users group, he can SFTP fine, but isn't chrooted.
>
> Using -vvv, I get the following:
>
> -----
> sam at localhost's password:
> debug3: packet_send2: adding 64 (len 56 padlen 8 extra_pad 64)
> debug2: we sent a password packet, wait for reply
> debug3: Wrote 144 bytes for a total of 1639
> debug1: Authentication succeeded (password).
> debug2: fd 4 setting O_NONBLOCK
> debug3: fd 5 is O_NONBLOCK
> debug1: channel 0: new [client-session]
> debug3: ssh_session2_open: channel_new: 0
> debug2: channel 0: send open
> debug1: Requesting no-more-sessions at openssh.com
> debug1: Entering interactive session.
> debug3: Wrote 128 bytes for a total of 1767
> debug2: callback start
> debug2: client_session2_setup: id 0
> debug1: Sending environment.
> debug3: Ignored env TERM
> debug3: Ignored env SHELL
> debug3: Ignored env SSH_CLIENT
> debug3: Ignored env SSH_TTY
> debug3: Ignored env USER
> debug3: Ignored env LS_COLORS
> debug3: Ignored env MAIL
> debug3: Ignored env PATH
> debug3: Ignored env PWD
> debug3: Ignored env SHLVL
> debug3: Ignored env HOME
> debug3: Ignored env LOGNAME
> debug3: Ignored env SSH_CONNECTION
> debug3: Ignored env LESSOPEN
> debug3: Ignored env LESSCLOSE
> debug3: Ignored env _
> debug1: Sending subsystem: sftp
> debug2: channel 0: request subsystem confirm 1
> debug2: fd 3 setting TCP_NODELAY
> debug2: callback done
> debug2: channel 0: open confirm rwindow 0 rmax 32768
> debug3: Wrote 64 bytes for a total of 1831
> debug2: channel 0: rcvd adjust 2097152
> debug2: channel_input_status_confirm: type 99 id 0
> debug2: subsystem request accepted on channel 0
> debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
> debug1: client_input_channel_req: channel 0 rtype eow at openssh.com reply 0
> debug2: channel 0: rcvd eow
> debug2: channel 0: close_read
> debug2: channel 0: input open -> closed
> debug2: channel 0: rcvd eof
> debug2: channel 0: output open -> drain
> debug2: channel 0: obuf empty
> debug2: channel 0: close_write
> debug2: channel 0: output drain -> closed
> debug2: channel 0: rcvd close
> debug3: channel 0: will not send data after close
> debug2: channel 0: almost dead
> debug2: channel 0: gc: notify user
> debug2: channel 0: gc: user detached
> debug2: channel 0: send close
> debug2: channel 0: is dead
> debug2: channel 0: garbage collecting
> debug1: channel 0: free: client-session, nchannels 1
> debug3: channel 0: status: The following connections are open:
>   #0 client-session (t4 r0 i3/0 o3/0 fd -1/-1 cfd -1)
>
> debug3: channel 0: close_fds r -1 w -1 e 6 c -1
> debug3: Wrote 32 bytes for a total of 1863
> debug3: Wrote 64 bytes for a total of 1927
> debug1: fd 0 clearing O_NONBLOCK
> debug3: fd 1 is not O_NONBLOCK
> Transferred: sent 1744, received 2008 bytes, in 0.0 seconds
> Bytes per second: sent 627347.0, received 722312.4
> debug1: Exit status 1
> Couldn't read packet: Connection reset by peer
> ------
>
> And if I change LogLevel to DEBUG2, I get this in /var/log/auth.log:
>
> ------
> ct  1 00:28:27 163-73-23 sshd[17728]: Accepted password for sam from
> 127.0.0.1 port 36128 ssh2
> Oct  1 00:28:27 163-73-23 sshd[17728]: debug1: monitor_child_preauth:
> sam has been authenticated by privileged process
> Oct  1 00:28:27 163-73-23 sshd[17728]: debug2: mac_setup: found hmac-md5
> Oct  1 00:28:27 163-73-23 sshd[17728]: debug2: mac_setup: found hmac-md5
> Oct  1 00:28:27 163-73-23 sshd[17731]: debug1: SELinux support disabled
> Oct  1 00:28:27 163-73-23 sshd[17728]: User child is on pid 17731
> Oct  1 00:28:27 163-73-23 sshd[17728]: debug1: do_cleanup
> ------
>
> What is going wrong? What else can I give you to troubleshoot?
>
> Thanks!
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