coder · sreya · Dec 5, 2024 · Nov 28, 2024 · Dec 2, 2024 · Dec 2, 2024
diff --git a/agent/agentexec/cli_linux.go b/agent/agentexec/cli_linux.go
@@ -15,6 +15,7 @@ import (
 
 	"golang.org/x/sys/unix"
 	"golang.org/x/xerrors"
+	"kernel.org/pub/linux/libs/security/libcap/cap"
 )
 
 // CLI runs the agent-exec command. It should only be called by the cli package.
@@ -48,6 +49,14 @@ func CLI() error {
 		return xerrors.Errorf("no exec command provided %+v", os.Args)
 	}
 
+	if *oom == unset {
+		// If an explicit oom score isn't set, we use the default.
+		*oom, err = defaultOOMScore()
+		if err != nil {
+			return xerrors.Errorf("get default oom score: %w", err)
+		}
+	}
+
 	if *nice == unset {
 		// If an explicit nice score isn't set, we use the default.
 		*nice, err = defaultNiceScore()
@@ -56,28 +65,42 @@ func CLI() error {
 		}
 	}
 
-	if *oom == unset {
-		// If an explicit oom score isn't set, we use the default.
-		*oom, err = defaultOOMScore()
-		if err != nil {
-			return xerrors.Errorf("get default oom score: %w", err)
-		}
+	// We drop effective caps prior to setting dumpable so that we limit the
+	// impact of someone attempting to hijack the process (i.e. with a debugger)
+	// to take advantage of the capabilities of the agent process.
+	err = dropEffectiveCaps()
+	if err != nil {
+		printfStdErr("failed to drop effective caps: %v", err)
 	}
 
-	err = unix.Setpriority(unix.PRIO_PROCESS, 0, *nice)
+	// Set dumpable to 1 so that we can adjust the oom score. If the process
+	// doesn't have capabilities or has an suid/sgid bit set, this is already
+	// set.
+	err = unix.Prctl(unix.PR_SET_DUMPABLE, 1, 0, 0, 0)
 	if err != nil {
-		// We alert the user instead of failing the command since it can be difficult to debug
-		// for a template admin otherwise. It's quite possible (and easy) to set an
-		// inappriopriate value for niceness.
-		printfStdErr("failed to adjust niceness to %d for cmd %+v: %v", *nice, args, err)
+		printfStdErr("failed to set dumpable: %v", err)
 	}
 
 	err = writeOOMScoreAdj(*oom)
 	if err != nil {
 		// We alert the user instead of failing the command since it can be difficult to debug
 		// for a template admin otherwise. It's quite possible (and easy) to set an
 		// inappriopriate value for oom_score_adj.
-		printfStdErr("failed to adjust oom score to %d for cmd %+v: %v", *oom, args, err)
+		printfStdErr("failed to adjust oom score to %d for cmd %+v: %v", *oom, execArgs(os.Args), err)
+	}
+
+	// Set dumpable back to 0 just to be safe. It's not inherited for execve anyways.
+	err = unix.Prctl(unix.PR_SET_DUMPABLE, 0, 0, 0, 0)
+	if err != nil {
+		printfStdErr("failed to unset dumpable: %v", err)
+	}
+
+	err = unix.Setpriority(unix.PRIO_PROCESS, 0, *nice)
+	if err != nil {
+		// We alert the user instead of failing the command since it can be difficult to debug
+		// for a template admin otherwise. It's quite possible (and easy) to set an
+		// inappriopriate value for niceness.
+		printfStdErr("failed to adjust niceness to %d for cmd %+v: %v", *nice, args, err)
 	}
 
 	path, err := exec.LookPath(args[0])
@@ -151,3 +174,16 @@ func execArgs(args []string) []string {
 func printfStdErr(format string, a ...any) {
 	_, _ = fmt.Fprintf(os.Stderr, "coder-agent: %s\n", fmt.Sprintf(format, a...))
 }
+
+func dropEffectiveCaps() error {
+	proc := cap.GetProc()
+	err := proc.ClearFlag(cap.Effective)
+	if err != nil {
+		return xerrors.Errorf("clear effective caps: %w", err)
+	}
+	err = proc.SetProc()
+	if err != nil {
+		return xerrors.Errorf("set proc: %w", err)
+	}
+	return nil
+}
diff --git a/go.mod b/go.mod
@@ -212,6 +212,7 @@ require (
 	github.com/google/go-github/v61 v61.0.0
 	github.com/mocktools/go-smtp-mock/v2 v2.4.0
 	github.com/natefinch/atomic v1.0.1
+	kernel.org/pub/linux/libs/security/libcap/cap v1.2.73
 )
 
 require (
@@ -248,6 +249,7 @@ require (
 	github.com/vmihailenco/msgpack/v5 v5.4.1 // indirect
 	github.com/vmihailenco/tagparser/v2 v2.0.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.54.0 // indirect
+	kernel.org/pub/linux/libs/security/libcap/psx v1.2.73 // indirect
 )
 
 require (

diff --git a/go.sum b/go.sum
@@ -1266,6 +1266,10 @@ howett.net/plist v1.0.0 h1:7CrbWYbPPO/PyNy38b2EB/+gYbjCe2DXBxgtOOZbSQM=
 howett.net/plist v1.0.0/go.mod h1:lqaXoTrLY4hg8tnEzNru53gicrbv7rrk+2xJA/7hw9g=
 inet.af/peercred v0.0.0-20210906144145-0893ea02156a h1:qdkS8Q5/i10xU2ArJMKYhVa1DORzBfYS/qA2UK2jheg=
 inet.af/peercred v0.0.0-20210906144145-0893ea02156a/go.mod h1:FjawnflS/udxX+SvpsMgZfdqx2aykOlkISeAsADi5IU=
+kernel.org/pub/linux/libs/security/libcap/cap v1.2.73 h1:Th2b8jljYqkyZKS3aD3N9VpYsQpHuXLgea+SZUIfODA=
+kernel.org/pub/linux/libs/security/libcap/cap v1.2.73/go.mod h1:hbeKwKcboEsxARYmcy/AdPVN11wmT/Wnpgv4k4ftyqY=
+kernel.org/pub/linux/libs/security/libcap/psx v1.2.73 h1:SEAEUiPVylTD4vqqi+vtGkSnXeP2FcRO3FoZB1MklMw=
+kernel.org/pub/linux/libs/security/libcap/psx v1.2.73/go.mod h1:+l6Ee2F59XiJ2I6WR5ObpC1utCQJZ/VLsEbQCD8RG24=
 lukechampine.com/uint128 v1.3.0 h1:cDdUVfRwDUDovz610ABgFD17nXD4/uDgVHl2sC3+sbo=
 lukechampine.com/uint128 v1.3.0/go.mod h1:c4eWIwlEGaxC/+H1VguhU4PHXNWDCDMUlWdIWl2j1gk=
 modernc.org/cc/v3 v3.41.0 h1:QoR1Sn3YWlmA1T4vLaKZfawdVtSiGx8H+cEojbC7v1Q=