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providers/linux: Fix linux Capabilities #196

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providers/linux: Fix linux Capabilities #196

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3 changes: 3 additions & 0 deletions .changelog/196.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
```release-note:bug
linux: fix linux capabilities
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As a reader of the release notes, I think I would prefer to have a few more details about what was broken.

```
18 changes: 7 additions & 11 deletions providers/linux/capabilities_linux.go
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Expand Up @@ -83,40 +83,36 @@ func capabilityName(num int) string {
return strconv.Itoa(num)
}

func readCapabilities(content []byte) (*types.CapabilityInfo, error) {
var cap types.CapabilityInfo

err := parseKeyValue(content, ':', func(key, value []byte) error {
func decodeCapabilityLine(content string, capInfo *types.CapabilityInfo) error {
return parseKeyValue([]byte(content), ':', func(key, value []byte) error {
var err error
switch string(key) {
case "CapInh":
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although this code was already like that, I debate inside me if it would add more value having all Cap* strings defined as constants. Feel free to ignore

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Ack, that makes sense, I was aiming to be conservative and using what's already there though.

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I made a little snippet that gets all of the CAPs if you think it might be helpful here

package main

import (
	"fmt"
	"go/constant"
	"go/types"
	"os"

	// "golang.org/x/sys/unix"
	"golang.org/x/tools/go/packages"
)

func main() {
	cfg := &packages.Config{Mode: packages.NeedTypes}
	pkgs, err := packages.Load(cfg, "golang.org/x/sys/unix")
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}

	caps := map[string]uint64{}

	for _, pkg := range pkgs {
		scope := pkg.Types.Scope()
		for _, t := range scope.Names() {
			if len(t) > 4 && t[0:4] == "CAP_" {
				t_v, err := types.Eval(pkg.Fset, pkg.Types, scope.Pos(), t)
				if err == nil {
					if flagbits, ok := constant.Uint64Val(t_v.Value); ok {
						caps[t] = flagbits
					}
				}
			}
		}
	}
	for key, val := range caps {
		fmt.Printf("%v: %v\n", key, val)
	}
}

cap.Inheritable, err = decodeBitMap(string(value), capabilityName)
capInfo.Inheritable, err = decodeBitMap(string(value), capabilityName)
if err != nil {
return err
}
case "CapPrm":
cap.Permitted, err = decodeBitMap(string(value), capabilityName)
capInfo.Permitted, err = decodeBitMap(string(value), capabilityName)
if err != nil {
return err
}
case "CapEff":
cap.Effective, err = decodeBitMap(string(value), capabilityName)
capInfo.Effective, err = decodeBitMap(string(value), capabilityName)
if err != nil {
return err
}
case "CapBnd":
cap.Bounding, err = decodeBitMap(string(value), capabilityName)
capInfo.Bounding, err = decodeBitMap(string(value), capabilityName)
if err != nil {
return err
}
case "CapAmb":
cap.Ambient, err = decodeBitMap(string(value), capabilityName)
capInfo.Ambient, err = decodeBitMap(string(value), capabilityName)
if err != nil {
return err
}
}
return nil
})

return &cap, err
}
21 changes: 19 additions & 2 deletions providers/linux/process_linux.go
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Expand Up @@ -18,6 +18,7 @@
package linux

import (
"bufio"
"bytes"
"io/ioutil"
"os"
Expand Down Expand Up @@ -213,13 +214,29 @@ func (p *process) Seccomp() (*types.SeccompInfo, error) {
return readSeccompFields(content)
}

// Returns error if at least one capability errored out, while still
// returning the successful ones
func (p *process) Capabilities() (*types.CapabilityInfo, error) {
content, err := ioutil.ReadFile(p.path("status"))
var gotErr error
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Recommend moving the declaration down closer to first usage to minimize scope.

f, err := os.OpenFile(p.path("status"), os.O_RDONLY, 0644)
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I think https://pkg.go.dev/os#Open would be more clear.

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absolutely, I'm new to Go so expect weirdness, I'll fix it.

if err != nil {
return nil, err
}
defer f.Close()
scanner := bufio.NewScanner(bufio.NewReader(f))
var capInfo types.CapabilityInfo
for scanner.Scan() {
line := scanner.Text()
if len(line) != 24 || line[:3] != "Cap" {
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Without ensuring the length of the line, then line[:3] could panic.

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Agreed, but it does check: if len(line) != 24 || line[:3] != "Cap"

continue
}
err = decodeCapabilityLine(line, &capInfo)
if err != nil && gotErr == nil {
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maybe we should do a "multierror" here? As it captures the error only for the first capability that fails and we lose the reason for any subsequent similar ones.

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hmm I'm ok with just returning the first one though, as it's 99.999999% (number took out of my hat) the reason of the possible subsequent failures

gotErr = err
}
}

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If the scanner encounters an error then Scan() will return false, and the you will only see the error if you call https://pkg.go.dev/bufio#Scanner.Err. So this needs to check for that error after the loop exits.

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Well spot, will fix it, many thanks

return readCapabilities(content)
return &capInfo, gotErr
}

func (p *process) User() (types.UserInfo, error) {
Expand Down
22 changes: 22 additions & 0 deletions system_test.go
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Expand Up @@ -310,3 +310,25 @@ func TestProcesses(t *testing.T) {
info.StartTime)
}
}

func TestCapabilities(t *testing.T) {
if runtime.GOOS != "linux" {
t.Skip("capabilities is linux only")
}
init, err := Process(1)
if err != nil {
t.Fatal(err)
}
v, ok := init.(types.Capabilities)
if !ok {
t.Fatal("capabilities is expected to be implemented for linux")
}
capInfo, err := v.Capabilities()
if err != nil {
t.Fatal(err)
}
totalCaps := 41
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@andrewkroh andrewkroh Dec 6, 2023 •
edited
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This seem brittle as it depends on the host operating system. The results could vary by kernel. Like if someone develops on an older OS then their tests might fail.

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Agreed, I wasn't sure if this is worth or not

assert.EqualValues(t, len(capInfo.Permitted), totalCaps)
assert.EqualValues(t, len(capInfo.Effective), totalCaps)
assert.EqualValues(t, len(capInfo.Bounding), totalCaps)
}