PcapOpenAdapter() appears to return ERROR_BAD_UNIT, not ERROR_ACCESS_DENIED, if the user says "No" to the UAC prompt
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- C
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Description
If the fix for issue #586 is applied to libpcap, so that pcap_create() doesn't fail if the user says "No" to the UAC prompt if Administrator privileges are required, the call to PcapOpenAdapter() in pcap_activate() appears to fail with ERROR_BAD_UNIT, which it interprets as "No such device", rather than with ERROR_ACCESS_DENIED, which it would interpret as "that device exists but you don't have permission to capture on it".
This, for example, causes tcpdump to report
tcpdump: \Device\NPF_{9080DB6C-2C39-480B-895F-49715A318BA0}: No such device exists
rather than reporting
tcpdump: \Device\NPF_{9080DB6C-2C39-480B-895F-49715A318BA0}: You don't have permission to capture on that device
which is more accurate.
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start in libpcap at pcap_activate() and the PcapOpenAdapter() call described in the issue, then review issue #586 for the related UAC behavior. Reproduce the declined UAC case and trace the returned error; done means the failure is interpreted as ERROR_ACCESS_DENIED so tcpdump reports a permissions error rather than "No such device exists."
Written by the indexing model from the issue text.
Assessment
- Tech stack
- c
- Domain
- networking
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100