Skip to content

fix uninitialised r0 register in the bpf program #383

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
tariq1890 wants to merge 1 commit into
base: main
Choose a base branch
from
Draft

fix uninitialised r0 register in the bpf program #383

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion src/nvcgo/internal/cgroup/v2.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -126,7 +126,7 @@ func (c *cgroupv2) AddDeviceRules(cgroupPath string, rules []DeviceRule) error {
// If no existing programs found, create a new program with just our device filter.
var newProgs []*ebpf.Program
if len(oldProgs) == 0 {
oldInsts := asm.Instructions{asm.Return()}
oldInsts := asm.Instructions{asm.Mov.Imm32(asm.R0, 1), asm.Return()}

@henry118 henry118 Jul 17, 2026

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

iiuc the return here is the no-match fallthrough (default rule).
Given we are doing a whitelist filter here, the default rule should be 0 (deny).

@tariq1890 tariq1890 Jul 17, 2026 •
edited
Loading

Copy link
Copy Markdown
Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I tried it with 0 initially. That led to a container create failed: open /dev/null: Operation not permitted

@henry118 henry118 Jul 17, 2026

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

that sounds incomplete whitelist. default with 1 essentially means no filter at all

@henry118 henry118 Jul 17, 2026

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

that makes me wonder if a race condition exists here since it's runc/crun who should have already whitelisted the common devices such as /dev/null. so in theory we shouldn't hit this code branch.

@tariq1890 tariq1890 Jul 17, 2026

Copy link
Copy Markdown
Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Got it. Right now, I've been testing this on an environment that uses cri-o and crun. Let me restart this cluster with cri-o+ runc instead.


newProg, err := generateNewProgram(rules, oldInsts)
if err != nil {
Expand Down