The ptrace method used by tracedump was my initial idea, but it has some drawbacks. If it does what you need, stick with it. If not, there’s another approach you can consider
The problem with using the ptrace approach is that it’s very invasive. Per the documentation of tracedump, some applications will crash under some circumstances. It’s very difficult to do this elegantly with ptrace without that risk
Another high-level approach would be to utilize network namespaces - essentially per-process containerized networking- with a virtual Ethernet device pair to route and mirror traffic
Using this approach, the traffic from your process will always route through a single point, separate from other processes, creating an opportunity to capture it
Roughly:
- Create a new network namespace
- Create and configure a virtual Ethernet device pair
- Set up forwarding from the namespace via the virtual Ethernet device pair, using iptables
- Set up tcpdump on one of the virtual Ethernet devices
- Finally, move the process of interest into the new network namespace
Optionally, you could also modify the traffic using this method. You would redirect the traffic to a userland forwarder outside of the namespace rather than routing it directly via iptables. That userland application would be responsible for sending the packets on to their final location
For more on this general idea, the best resources would probably be guides on “transpart proxying”, even though most of those use-cases involve (effectively) rewriting a packet so that it uses a socks or http proxy to reach its destination (something you won’t want, except for certain types of applications)
There are plenty of potential problems with this approach, depending on the details of what you need to do and how the process communicates and operates. For example, potential problems may be:
- Handling traffic that goes to loopback
- Handling the case where the process forks, and you don’t want to capture the traffic of the child
- … plenty of other exceptional cases
So YMMV
Here are a few posts/docs that may help to understand this if you’re not familiar with it:
... they don’t perfectly fit your use-case, but they’re very closely related and they demonstrate the commands required to do per-process network isolation
I’m curious if there are any projects out there that help to automate this in a user-friendly way. I’ll add a reference if I find one as I currently do this manually, case-by-case