From 67674e59a6dfd011820535773b98d1474651c5a5 Mon Sep 17 00:00:00 2001
From: Christian Franke <nobody@nowhere.ws>
Date: Thu, 4 Dec 2014 00:27:19 +0100
Subject: [PATCH] Drop privileges

---
 picocom.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/picocom.c b/picocom.c
index 02ddb5d..23235a2 100644
--- a/picocom.c
+++ b/picocom.c
@@ -30,12 +30,17 @@
 #include <errno.h>
 #include <assert.h>
 #include <stdarg.h>
+#include <stddef.h>
 #include <signal.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
+#include <sys/prctl.h>
+#include <sys/syscall.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
 #include <limits.h>
 
 #define _GNU_SOURCE
@@ -1151,6 +1156,31 @@ parse_args(int argc, char *argv[])
 
 /**********************************************************************/
 
+static void do_seccomp(void)
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD+BPF_W+BPF_ABS, offsetof(struct seccomp_data, nr)),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 9, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_ioctl, 8, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_nanosleep, 7, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 6, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigaction, 5, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigprocmask, 4, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_select, 3, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_unlink, 2, 0),
+		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 1, 0),
+		BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
+		BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
+	};
+
+	struct sock_fprog prog = {
+		.len = sizeof(filter) / sizeof(filter[0]),
+		.filter = filter
+	};
+
+	if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog))
+		fatal("Could not drop privileges!");
+}
 
 int
 main(int argc, char *argv[])
@@ -1206,6 +1236,9 @@ main(int argc, char *argv[])
 			  term_strerror(term_errno, errno));
 
 	fd_printf(STO, "Terminal ready\r\n");
+
+	do_seccomp();
+
 	loop();
 
 	fd_printf(STO, "\r\n");
-- 
2.1.1