Segfault when calling append-rule command

[tweksteen]

This was observed on 0.7.4 when called with: $ usbguard append-rule 'allow id 1d6b:0002 serial "0000:00:1a.0" name "EHCI Host Controller" with-interface 09:00:00'

kernel: [15672304.755564] usbguard[191461]: segfault at 7f6838622008 ip 00007f68373b919d sp 00007fff8bdac510 error 4 in libc-2.28.so[7f6837335000+1b5000] kernel: [15672304.755571] Code: 89 ee 48 89 df 5b 5d e9 11 fd ff ff 90 53 48 83 ec 10 48 8b 05 6c 4d 33 00 48 8b 00 48 85 c0 0f 85 88 00 00 00 48 85 ff 74 73 <48> 8b 47 f8 48 8d 77 f0 a8 02 75 37 48 8b 15 c8 4b 33 00 64 48 83

Tracing the segfault, this is triggered within free(), which makes me think a double-free is happening somewhere. I don't have further details and was not able to reproduce after that. There has not been large code changes between 0.7.4 and master on the codepath for that command (CLI, IPC Client), which makes me think this is still valid for the current version.