[luka-n]

re #18

[frederikmoellers]

There seems to be a bug with (at least) xscreensaver under Debian stretch. When using pam_usb for authentication only (no agent functionality like automatic screen unlock), it sometimes hangs during udisks_client_get_object_manager in device.c:41. I'm still trying to figure out what exactly goes wrong there, just FYI.

[aluzzardi]

@luka-n, could you remove those? They are editor specific and I don't think they belong in the source file.

[nazar-pc]

@luka-n, can you respond to comments in this PR so that we can get it merged and (possibly) even back to Ubuntu repository?

[drmfinlay]

Hey. I was looking into this and I noticed that another fork of this repo has most of these issues fixed. Plus it doesn't appear to have the problem with xscreensaver that @frederikmoellers mentioned above, which was an issue for me too, at least under Linux Mint 18. Perhaps a pull request from that fork's master branch would be a better idea. I could fix the problems @aluzzardi commented on above that are not fixed in that fork and make a new pull request.

[aluzzardi]

Please do - happy to review & merge

[andrey-utkin]

it doesn't appear to have the problem with xscreensaver that @frederikmoellers mentioned above

In your PR there is still such problem.

It works first time, but hangs a second time.

Sep 25 14:39:36 starlite pam_usb[11787]: pam_usb v0.5.0
Sep 25 14:39:36 starlite pam_usb[11787]: Authentication request for user "j" (xscreensaver)
Sep 25 14:39:36 starlite pam_usb[11787]: deny_remote is disabled. Skipping local check.
Sep 25 14:39:36 starlite pam_usb[11787]: Searching for "/dev/sdb2" in the hardware database...
Sep 25 14:39:36 starlite pam_usb[11787]: Device "/dev/sdb2" is not connected (bad).
Sep 25 14:39:36 starlite pam_usb[11787]: Access denied.
Sep 25 14:39:50 starlite pam_usb[11787]: pam_usb v0.5.0
Sep 25 14:39:50 starlite pam_usb[11787]: Authentication request for user "j" (xscreensaver)
Sep 25 14:39:50 starlite pam_usb[11787]: deny_remote is disabled. Skipping local check.

apparently after last line, "Searching for ..." should appear, but this never happens.

 $ gdb -p 16259
Password:
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and "show warranty" for details.
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Type "show configuration" for configuration details.
For bug reporting instructions, please see:
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For help, type "help".
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Attaching to process 16259
[New LWP 16294]
[New LWP 16295]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
0x00007f15050fa829 in syscall () from /lib64/libc.so.6
(gdb) info threads
  Id   Target Id         Frame
* 1    Thread 0x7f1506b93780 (LWP 16259) "xscreensaver" 0x00007f15050fa829 in syscall () from /lib64/libc.so.6
  2    Thread 0x7f14fdbb9700 (LWP 16294) "gmain" 0x00007f15050f48dd in poll () from /lib64/libc.so.6
  3    Thread 0x7f14fd3b8700 (LWP 16295) "gdbus" 0x00007f15050f48dd in poll () from /lib64/libc.so.6
(gdb) bt
#0  0x00007f15050fa829 in syscall () from /lib64/libc.so.6
#1  0x00007f1501d4ea7d in g_cond_wait () from /usr/lib64/libglib-2.0.so.0
#2  0x00007f1501d384c4 in g_once_init_enter () from /usr/lib64/libglib-2.0.so.0
#3  0x00007f15025c7492 in udisks_client_get_type () from /usr/lib64/libudisks2.so.0
#4  0x00007f15025c7a3a in udisks_client_get_object_manager () from /usr/lib64/libudisks2.so.0
#5  0x00007f1502b1dc10 in pusb_device_check () from /lib64/security/pam_usb.so
#6  0x00007f1502b1df62 in pam_sm_authenticate () from /lib64/security/pam_usb.so
#7  0x00007f15055f2ebe in ?? () from /lib64/libpam.so.0
#8  0x00007f15055f27be in pam_authenticate () from /lib64/libpam.so.0
#9  0x0000563df3de1514 in ?? ()
#10 0x0000563df3de0d0a in ?? ()
#11 0x0000563df3de083f in ?? ()
#12 0x0000563df3dcca7d in ?? ()
#13 0x00007f1505027521 in __libc_start_main () from /lib64/libc.so.6
#14 0x0000563df3dcccaa in ?? ()
(gdb) 

I couldn't find any refcounting bug in src/device.c. Making manager allocation one-time with making it static doesn't seem to work, too.

[andrey-utkin]

Published a small improvement iamsivil#4 , but it doesn't help the bug described above.
I have worked around my issue by calling pam_exec instead:

auth            sufficient      pam_exec.so quiet /usr/bin/pamusb-check my-user-name
auth 	include		system-auth

Sorry for hijacking this thread. I'm done now.

[drmfinlay]

Ah yes. Sorry, I noticed that bug was still there some time after writing that and forgot to mention it I guess.
I see what you mean about 'Searching for...' not appearing. I might look into that tomorrow.
Thanks for the workaround though. It works for me, but I'm not really 100% on why it works.

[andrey-utkin]

The workaround works apparently becasue spawned pamusb-check process opens udisks resources just one in its lifetime, and exits. While in case of calling pam_usb through PAM API, same xscreensaver process does it again. Looks like resources recycling bug somewhere, maybe even udisks, because i reviewed src/device.c extensively and it looks fine in regard to refcounting etc.

[drmfinlay]

Ah right, that makes sense. I had thought the bug was external to pam_usb. If it is a udisks issue, then I'm wondering if it's fixed in more recent versions. I'm running udisks 2.1.8 (a little dated) on Debian 9. I'll try testing with a more recent version and see if I can confirm this.

By the way, have you given any thought to using an alternative to udisks2 (re: #36)?

I'm now also sorry for hijacking this thread.. Should we continue this elsewhere..?