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Additional systemd service hardening #11

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Additional systemd service hardening #11

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candrews
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Add ProtectSystem=full, NoNewPrivileges=true, PrivateDevices=true, and a restricted CapabilityBoundingSet.

There's no reason to comment out any of these options - according to the systemd documentation at https://www.freedesktop.org/software/systemd/man/systemd.unit.html :

If systemd encounters an unknown option, it will write a warning log message but continue loading the unit.

So it's fine to leave in options that older versions may not understand - they'll simply be ignored.

@candrews
Additional systemd service hardening
cc1e73e 
Add ProtectSystem=full, NoNewPrivileges=true, PrivateDevices=true, and a restricted CapabilityBoundingSet.

There's no reason to comment out any of these options - according to the systemd documentation at https://www.freedesktop.org/software/systemd/man/systemd.unit.html :
> If systemd encounters an unknown option, it will write a warning log message but continue loading the unit.

So it's fine to leave in options that older versions may not understand - they'll simply be ignored.
cmouse
cmouse reviewed Aug 5, 2016
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dovecot.service.in
ProtectSystem=full
NoNewPrivileges=true
PrivateDevices=true
CapabilityBoundingSet=CAP_CHOWN CAP_DAC_OVERRIDE CAP_IPC_LOCK CAP_KILL CAP_NET_BIND_SERVICE CAP_SETGID CAP_SETUID CAP_SYS_CHROOT
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This might lack some caps.

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Any thoughts on what caps may be missing?

And what makes you think there may be some missing? Is there a problem that you see when you use this service unit?

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I'll test these.

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NoNewPrivileges prevents UID changes, and we need to do UID changes. I need to adapt this.

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@cmouse I don't think NoNewPrivileges prevents UID changes - it prevents increasing privileges once they've been lost. If, for example, dovecot starts as root, then drops privileges and changes UID to dovecot, that would be fine. If, on the other hand, dovecot starts as root, then drops privileges and changes UID to dovecot, then tries to regain dropped privileges, then NoNewPrivileges would block that.

I'm curious - is there a problem that you're seeing? I'd be really interested in knowing what the problem may be.

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I have not yet properly tried it, but in some cases some dovecot processes need to change their EUID to some user, and then back to root, and again to some other user. I'll try this out with this systemd unit and see if it really works.

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After testing it, it was missing CAP_SYS_RESOURCE. Seems that NoNewPrivileges at least initially works with environment with multiple UIDs for users.

Sep 19 09:03:52 cypher dovecot[10585]: master: Error: setrlimit(RLIMIT_NPROC, 4390): Operation not permitted

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Looks like you already made these changes, thanks!
563c1e3

@candrews candrews closed this Aug 20, 2016
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cmouse commented Aug 20, 2016 •
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Yes forgot to close this. Streamlined these into other changes. Thank you for your contribution.

DovecotSync pushed a commit that referenced this pull request Jul 9, 2019
@stephanbosch @sirainen
lib-http: guard against hshared use-after-free
6236f36 
This fixes a race condition where the http_client_host_shared_idle_timeout()
function would get called with an already freed hshared argument.

Specifically, the situation arises from the hshared idle timeout calling
http_client_host_shared_free(), which removes the timeout and then proceeds to
free the client queue.  The client queue freeing code indirectly calls
http_client_host_shared_check_idle(), which notices that there is no idle
timeout and allocates one.

The backtrace at the point of this new timeout allocation:

    frame #3: 0x00007f0c775897f0 libdovecot.so.0`timeout_add_to(...) ioloop.c:280
    frame #4: 0x00007f0c7751a45f libdovecot.so.0`http_client_host_shared_check_idle(hshared=<unavailable>) at http-client-host.c:69
    frame #5: 0x00007f0c7750de89 libdovecot.so.0`http_client_request_error(_req=<unavailable>, status=9000, error="") at http-client-request.c:1525
    frame #6: 0x00007f0c77517f38 libdovecot.so.0`http_client_queue_fail_full(queue=0x000055e13cff0e10, status=9000, error="", all=<unavailable>) at http-client-queue.c:183
    frame #7: 0x00007f0c77518baa libdovecot.so.0`http_client_queue_free(queue=0x000055e13cff0e10) at http-client-queue.c:141
    frame #8: 0x00007f0c7751a8bc libdovecot.so.0`http_client_host_free_shared(_host=<unavailable>) at http-client-host.c:391
    frame #9: 0x00007f0c7751ab4c libdovecot.so.0`http_client_host_shared_free(_hshared=0x00007ffdac109e48) at http-client-host.c:294
    frame #10: 0x00007f0c7751ace8 libdovecot.so.0`http_client_host_shared_idle_timeout(hshared=<unavailable>) at http-client-host.c:40
    frame #11: 0x00007f0c7758a1a4 libdovecot.so.0`io_loop_handle_timeouts at ioloop.c:682
    frame #12: 0x00007f0c7758a089 libdovecot.so.0`io_loop_handle_timeouts(ioloop=0x000055e13cfc8d80) at ioloop.c:696
    frame #13: 0x00007f0c7758befc libdovecot.so.0`io_loop_handler_run_internal(ioloop=0x000055e13cfc8d80) at ioloop-select.c:126
    frame #14: 0x00007f0c7758a56d libdovecot.so.0`io_loop_handler_run(ioloop=<unavailable>) at ioloop.c:767
    frame #15: 0x00007f0c7758a798 libdovecot.so.0`io_loop_run(ioloop=0x000055e13cfc8d80) at ioloop.c:740
    frame #16: 0x00007f0c774f61eb libdovecot.so.0`master_service_run(service=0x000055e13cfc8c10, callback=<unavailable>) at master-service.c:782
    frame #17: 0x000055e13b48e3a5 stats`main(argc=<unavailable>, argv=<unavailable>) at main.c:99
    frame #18: 0x00007f0c771092e1 libc.so.6`__libc_start_main + 241
    frame #19: 0x000055e13b48e41a stats`_start + 42
DovecotSync pushed a commit that referenced this pull request Jul 9, 2019
@stephanbosch
lib-http: guard against hshared use-after-free
4083c73 
This fixes a race condition where the http_client_host_shared_idle_timeout()
function would get called with an already freed hshared argument.

Specifically, the situation arises from the hshared idle timeout calling
http_client_host_shared_free(), which removes the timeout and then proceeds to
free the client queue.  The client queue freeing code indirectly calls
http_client_host_shared_check_idle(), which notices that there is no idle
timeout and allocates one.

The backtrace at the point of this new timeout allocation:

    frame #3: 0x00007f0c775897f0 libdovecot.so.0`timeout_add_to(...) ioloop.c:280
    frame #4: 0x00007f0c7751a45f libdovecot.so.0`http_client_host_shared_check_idle(hshared=<unavailable>) at http-client-host.c:69
    frame #5: 0x00007f0c7750de89 libdovecot.so.0`http_client_request_error(_req=<unavailable>, status=9000, error="") at http-client-request.c:1525
    frame #6: 0x00007f0c77517f38 libdovecot.so.0`http_client_queue_fail_full(queue=0x000055e13cff0e10, status=9000, error="", all=<unavailable>) at http-client-queue.c:183
    frame #7: 0x00007f0c77518baa libdovecot.so.0`http_client_queue_free(queue=0x000055e13cff0e10) at http-client-queue.c:141
    frame #8: 0x00007f0c7751a8bc libdovecot.so.0`http_client_host_free_shared(_host=<unavailable>) at http-client-host.c:391
    frame #9: 0x00007f0c7751ab4c libdovecot.so.0`http_client_host_shared_free(_hshared=0x00007ffdac109e48) at http-client-host.c:294
    frame #10: 0x00007f0c7751ace8 libdovecot.so.0`http_client_host_shared_idle_timeout(hshared=<unavailable>) at http-client-host.c:40
    frame #11: 0x00007f0c7758a1a4 libdovecot.so.0`io_loop_handle_timeouts at ioloop.c:682
    frame #12: 0x00007f0c7758a089 libdovecot.so.0`io_loop_handle_timeouts(ioloop=0x000055e13cfc8d80) at ioloop.c:696
    frame #13: 0x00007f0c7758befc libdovecot.so.0`io_loop_handler_run_internal(ioloop=0x000055e13cfc8d80) at ioloop-select.c:126
    frame #14: 0x00007f0c7758a56d libdovecot.so.0`io_loop_handler_run(ioloop=<unavailable>) at ioloop.c:767
    frame #15: 0x00007f0c7758a798 libdovecot.so.0`io_loop_run(ioloop=0x000055e13cfc8d80) at ioloop.c:740
    frame #16: 0x00007f0c774f61eb libdovecot.so.0`master_service_run(service=0x000055e13cfc8c10, callback=<unavailable>) at master-service.c:782
    frame #17: 0x000055e13b48e3a5 stats`main(argc=<unavailable>, argv=<unavailable>) at main.c:99
    frame #18: 0x00007f0c771092e1 libc.so.6`__libc_start_main + 241
    frame #19: 0x000055e13b48e41a stats`_start + 42
DovecotSync pushed a commit that referenced this pull request Jul 12, 2019
@stephanbosch
lib-http: guard against hshared use-after-free
7896f07 
This fixes a race condition where the http_client_host_shared_idle_timeout()
function would get called with an already freed hshared argument.

Specifically, the situation arises from the hshared idle timeout calling
http_client_host_shared_free(), which removes the timeout and then proceeds to
free the client queue.  The client queue freeing code indirectly calls
http_client_host_shared_check_idle(), which notices that there is no idle
timeout and allocates one.

The backtrace at the point of this new timeout allocation:

    frame #3: 0x00007f0c775897f0 libdovecot.so.0`timeout_add_to(...) ioloop.c:280
    frame #4: 0x00007f0c7751a45f libdovecot.so.0`http_client_host_shared_check_idle(hshared=<unavailable>) at http-client-host.c:69
    frame #5: 0x00007f0c7750de89 libdovecot.so.0`http_client_request_error(_req=<unavailable>, status=9000, error="") at http-client-request.c:1525
    frame #6: 0x00007f0c77517f38 libdovecot.so.0`http_client_queue_fail_full(queue=0x000055e13cff0e10, status=9000, error="", all=<unavailable>) at http-client-queue.c:183
    frame #7: 0x00007f0c77518baa libdovecot.so.0`http_client_queue_free(queue=0x000055e13cff0e10) at http-client-queue.c:141
    frame #8: 0x00007f0c7751a8bc libdovecot.so.0`http_client_host_free_shared(_host=<unavailable>) at http-client-host.c:391
    frame #9: 0x00007f0c7751ab4c libdovecot.so.0`http_client_host_shared_free(_hshared=0x00007ffdac109e48) at http-client-host.c:294
    frame #10: 0x00007f0c7751ace8 libdovecot.so.0`http_client_host_shared_idle_timeout(hshared=<unavailable>) at http-client-host.c:40
    frame #11: 0x00007f0c7758a1a4 libdovecot.so.0`io_loop_handle_timeouts at ioloop.c:682
    frame #12: 0x00007f0c7758a089 libdovecot.so.0`io_loop_handle_timeouts(ioloop=0x000055e13cfc8d80) at ioloop.c:696
    frame #13: 0x00007f0c7758befc libdovecot.so.0`io_loop_handler_run_internal(ioloop=0x000055e13cfc8d80) at ioloop-select.c:126
    frame #14: 0x00007f0c7758a56d libdovecot.so.0`io_loop_handler_run(ioloop=<unavailable>) at ioloop.c:767
    frame #15: 0x00007f0c7758a798 libdovecot.so.0`io_loop_run(ioloop=0x000055e13cfc8d80) at ioloop.c:740
    frame #16: 0x00007f0c774f61eb libdovecot.so.0`master_service_run(service=0x000055e13cfc8c10, callback=<unavailable>) at master-service.c:782
    frame #17: 0x000055e13b48e3a5 stats`main(argc=<unavailable>, argv=<unavailable>) at main.c:99
    frame #18: 0x00007f0c771092e1 libc.so.6`__libc_start_main + 241
    frame #19: 0x000055e13b48e41a stats`_start + 42
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@candrews @cmouse