Hi,

On 28.06.2016 15:21, Jamie Strandboge wrote:
On Tue, 2016-06-28 at 10:44 +0200, Pawel Stolowski wrote:
Hi,

I've been trying to create a snap package for Scid-vs-PC (and old-style
TCL/TK based app) but have only been able to get it working in devmode.
In the strict mode it crashes in libtk8.6.so and the segfault appears
right after a denied access to read "/lib", in dmesg which makes me
think that tcl/tk doesn't handle such (unexpected) scenario very well.

When running in the devmode I get:
[ 4039.752903] audit: type=1400 audit(1467102032.459:56):
apparmor="ALLOWED" operation="open" profile="snap.scid-vs-pc.scidvspc"
name="/lib/" pid=18523 comm="tkscid" requested_mask="r" denied_mask="r"
fsuid=1000 ouid=0
(and the app runs fine).

I suspect that just making "/lib" readable to my snap would make that
app happy, so a couple of questions:
- can I somehow expose "/lib" in read-only mode to my snap under
"strict" confinement?
- or can I somehow simulate the presence of "/lib" (and let it be empty)?
Can you file a bug and add the 'snapd-interface' tag? For now you can workaround
this in strict mode by adding to /var/lib/snapd/apparmor/profiles/snap.scid-vs-
pc.scidvspc:

   /lib/ r, # trailing '/' is important

then do:
$ sudo apparmor_parser -r /var/lib/snapd/apparmor/profiles/snap.scid-vs-
pc.scidvspc

Then try again. Depending on what the program does, you might have to add
'/usr/lib/', '/usr/local/lib/', etc. Please report all the accesses needed in
the bug and I can get this fixed up.
Ok, here you go: https://bugs.launchpad.net/snappy/+bug/1597259. I've only seen it with /lib so far.

Now, it seems the real problem is not with /lib access, but it's font-related... After succesfully running the app in devmode yesterday, this morning after booting my PC it doesn't work anymore :O, looks like I was just lucky yesterday and the app is unstable due to a problem with fonts. I managed to run it with gdb inside the container and got this stacktrace on crash:

#0 0x00007ffff759ee53 in TkpGetFontFamilies () from /snap/scid-vs-pc/x2/lib/libtk8.6.so #1 0x00007ffff74f3dc5 in Tk_FontObjCmd () from /snap/scid-vs-pc/x2/lib/libtk8.6.so #2 0x00007ffff7848e07 in TclNRRunCallbacks () from /snap/scid-vs-pc/x2/lib/libtcl8.6.so #3 0x00007ffff784ae75 in TclEvalEx () from /snap/scid-vs-pc/x2/lib/libtcl8.6.so #4 0x00007ffff7902908 in Tcl_FSEvalFileEx () from /snap/scid-vs-pc/x2/lib/libtcl8.6.so #5 0x00007ffff74fca9e in Tk_MainEx () from /snap/scid-vs-pc/x2/lib/libtk8.6.so
#6  0x00000000004045aa in main ()

I'm trying to guess what font-related stuff may be missing. I've the following packages installed via stage-packages:
- ttf-ubuntu-font-family
- xfonts-base
- xfonts-scalable
- fontconfig-config

Any idea what else to try?

Thanks,
Pawel



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