update: add open_by_handle_at syscall

[Andreagit97]

What type of PR is this?

/kind feature

Any specific area of the project related to this PR?

/area driver-kmod

/area driver-ebpf

/area libscap

/area libsinsp

What this PR does / why we need it:

This adds support to the open_by_handle_at syscall. This has been reported as a high priority missing syscall in the "umbrella issue" 👇

falcosecurity/falco#676

Which issue(s) this PR fixes:

Special notes for your reviewer:

The following sample program has been used for testing:

main.c.txt

1. Compile main.c:

gcc main.c -o main

2. Create the file to open where you want.

3. Run main passing as argument the absolute file path or the path relative to the current working directory of the calling process:

./main <path>

Open_by_hanlde_at path extraction

We have chosen to extract the absolute path of the opened file from the file descriptor returned by the syscall. In case of error, the file descriptor is not valid so unfortunately, we cannot extract the file path. The file descriptor seems the smartest way to extract information about the path, given the little information provided by the syscall.

Bpf testing

I have tested the new bpf features on the following vagrant images:

1. Image = bento/amazonlinux-2

• Kernel = 4.14.198-152.320.amzn2.x86_64
• clang = clang version 11.1.0

2. Image = generic/debian10

• Kernel = 4.19.0-18-amd64
• clang = clang version 7.0.1-8+deb10u2

3. Image = generic/centos8

• Kernel = 4.18.0-348.2.1.el8_5.x86_64
• clang = clang version 12.0.1

4. Image = generic/fedora33

• Kernel = 5.14.18-100.fc33.x86_64
• clang = clang version 11.0.0 (Fedora 11.0.0-3.fc33)

5. Image = generic/alpine314

• Kernel = 5.10.82
• clang = clang version 11.1.0

6. Image = bento/ubuntu-20.10

• Kernel = 5.8.0-63-generic
• clang = clang version 11.0.0-2

7. Image = bento/ubuntu-21.04

• Kernel = 5.14.0-051400-generic
• clang = clang version 12.0.0

8. Image = opensuse/Tumbleweed.x86_64

• Kernel = 5.15.6
• clang = clang version 13.0.0

Old kernels verifiers (like 4.14) allow reading only file paths consisting of at most 16 components. With more than 16 components the verifier complains about the excessive bpf program length due to the loop unrolling approach used in the new bpf_get_path function. The function bpf_get_path added in this pull request, is an attempt to collect the file path from the file descriptor. Kernel 5.10 introduced a new bpf_helper called bpf_d_path which however cannot be used by BPF_PROG_TYPE_RAW_TRACEPOINT programs. Unfortunately, in our case, libscap loads all bpf programs as BPF_PROG_TYPE_RAW_TRACEPOINT.

Does this PR introduce a user-facing change?:

update: add support for `open_by_handle_at` syscall

[poiana]

Hi @Andreagit97. Thanks for your PR.

I'm waiting for a falcosecurity member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[jasondellaluce]

Great work! Left a couple of comments.

[leogr]

/ok-to-test

[leogr]

/approve

[poiana]

LGTM label has been added.

Git tree hash: 4deec2c4aac411d09ff71f3647d52fcb6a8a423c

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Andreagit97, leogr

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