From 0750245eea6b2b4dd4bb4f4f974beeb2a900c1d6 Mon Sep 17 00:00:00 2001
From: Dmitry Vyukov <dvyukov@google.com>
Date: Tue, 20 Oct 2015 17:43:02 +0200
Subject: experimental functionality to impersonate nobody user in executor

---
 executor/executor.cc | 28 +++++++++++++++++++++++++++-
 ipc/ipc.go           | 14 +++++++++++++-
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/executor/executor.cc b/executor/executor.cc
index a8804994a..a266f54c1 100644
--- a/executor/executor.cc
+++ b/executor/executor.cc
@@ -16,6 +16,7 @@
 #include <sys/stat.h>
 #include <sys/mman.h>
 #include <pthread.h>
+#include <grp.h>
 #include <algorithm>
 #include "syscalls.h"
 
@@ -45,6 +46,7 @@ bool flag_debug;
 bool flag_cover;
 bool flag_threaded;
 bool flag_deduplicate;
+bool flag_drop_privs;
 
 __attribute__((aligned(64 << 10))) char input_data[kMaxInput];
 __attribute__((aligned(64 << 10))) char output_data[kMaxOutput];
@@ -81,6 +83,7 @@ int cover_fd;
 
 __attribute__((noreturn)) void fail(const char* msg, ...);
 __attribute__((noreturn)) void error(const char* msg, ...);
+__attribute__((noreturn)) void exitf(const char* msg, ...);
 void debug(const char* msg, ...);
 uint64_t read_input(uint64_t** input_posp);
 uint64_t read_arg(uint64_t** input_posp);
@@ -111,6 +114,7 @@ int main()
 	flag_cover = flags & (1 << 1);
 	flag_threaded = flags & (1 << 2);
 	flag_deduplicate = flags & (1 << 3);
+	flag_drop_privs = flags & (1 << 4);
 	output_pos = (uint32_t*)&output_data[0];
 	write_output(0); // Number of executed syscalls (updated later).
 
@@ -118,6 +122,16 @@ int main()
 	if (!flag_threaded)
 		cover_init(&threads[0]);
 
+	if (flag_drop_privs) {
+		// TODO: 65534 is meant to be nobody
+		if (setgroups(0, NULL))
+			fail("failed to setgroups");
+		if (setresgid(65534, 65534, 65534))
+			fail("failed to setresgid");
+		if (setresuid(65534, 65534, 65534))
+			fail("failed to setresuid");
+	}
+
 	int call_index = 0;
 	for (int n = 0;; n++) {
 		uint64_t call_num = read_input(&input_pos);
@@ -212,7 +226,7 @@ thread_t* schedule_call(int n, int call_index, int call_num, uint64_t num_args,
 			th->handled = true;
 			if (flag_threaded) {
 				if (pthread_create(&th->th, 0, worker_thread, th))
-					fail("pthread_create failed");
+					exitf("pthread_create failed");
 			}
 		}
 		if (__atomic_load_n(&th->done, __ATOMIC_ACQUIRE)) {
@@ -496,6 +510,18 @@ void error(const char* msg, ...)
 	exit(68);
 }
 
+// just exit (e.g. due to temporal ENOMEM error)
+void exitf(const char* msg, ...)
+{
+	fflush(stdout);
+	va_list args;
+	va_start(args, msg);
+	vfprintf(stderr, msg, args);
+	va_end(args);
+	fprintf(stderr, "\n");
+	exit(1);
+}
+
 void debug(const char* msg, ...)
 {
 	if (!flag_debug)
diff --git a/ipc/ipc.go b/ipc/ipc.go
index 511398a7f..44a232048 100644
--- a/ipc/ipc.go
+++ b/ipc/ipc.go
@@ -34,6 +34,7 @@ const (
 	FlagCover                          // collect coverage
 	FlagThreaded                       // use multiple threads to mitigate blocked syscalls
 	FlagDedupCover                     // deduplicate coverage in executor
+	FlagDropPrivs                      // impersonate nobody user
 	FlagStrace                         // run executor under strace
 )
 
@@ -42,11 +43,20 @@ func MakeEnv(bin string, timeout time.Duration, flags uint64) (*Env, error) {
 	if err != nil {
 		return nil, err
 	}
+	defer func() {
+		if inf != nil {
+			closeMapping(inf, inmem)
+		}
+	}()
 	outf, outmem, err := createMapping(16 << 20)
 	if err != nil {
-		closeMapping(inf, inmem)
 		return nil, err
 	}
+	defer func() {
+		if outf != nil {
+			closeMapping(outf, outmem)
+		}
+	}()
 	for i := 0; i < 8; i++ {
 		inmem[i] = byte(flags >> (8 * uint(i)))
 	}
@@ -63,6 +73,8 @@ func MakeEnv(bin string, timeout time.Duration, flags uint64) (*Env, error) {
 	if len(env.bin) == 0 {
 		return nil, fmt.Errorf("binary is empty string")
 	}
+	inf = nil
+	outf = nil
 	return env, nil
 }
 
-- 
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