organize examples

This commit is largely based on work by Thiago Arrais (@thiagoarrais)
and Shane Bradfield (@l33tLumberjack). I wasn't really able to get their
PR reasonably merged onto the latest master, so I reapplied their changes
manually here and did some further improvements on that.

1 files changed, 87 insertions, 0 deletions

diff --git a/examples/complex/full_transparency_shim.c b/examples/complex/full_transparency_shim.c
new file mode 100644
index 00000000..923eea76
--- /dev/null
+++ b/examples/complex/full_transparency_shim.c
@@ -0,0 +1,87 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/types.h>
+#include <sys/capability.h>
+#include <unistd.h>
+#include <errno.h>
+
+/* This setuid wrapper can be used to run mitmproxy in full transparency mode, as a normal user.
+ * It will set the required capabilities (CAP_NET_RAW), drop privileges, and will then run argv[1]
+ * with the same capabilities.
+ *
+ * It can be compiled as follows:
+ * gcc examples/mitmproxy_shim.c -o mitmproxy_shim -lcap
+*/
+
+int set_caps(cap_t cap_struct, cap_value_t *cap_list, size_t bufsize) {
+	int cap_count = bufsize / sizeof(cap_list[0]);
+
+	if (cap_set_flag(cap_struct, CAP_PERMITTED, cap_count, cap_list, CAP_SET) ||
+            cap_set_flag(cap_struct, CAP_EFFECTIVE, cap_count, cap_list, CAP_SET) ||
+            cap_set_flag(cap_struct, CAP_INHERITABLE, cap_count, cap_list, CAP_SET)) {
+		if (cap_count < 2) {
+			fprintf(stderr, "Cannot manipulate capability data structure as user: %s.\n", strerror(errno));
+		} else {
+			fprintf(stderr, "Cannot manipulate capability data structure as root: %s.\n", strerror(errno));
+		}
+		return -1;
+	}
+
+	if (cap_count < 2) {
+		if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_RAW, 0, 0)) {
+			fprintf(stderr, "Failed to add CAP_NET_RAW to the ambient set: %s.\n", strerror(errno));
+			return -2;
+		}
+	}
+
+	if (cap_set_proc(cap_struct)) {
+		if (cap_count < 2) {
+			fprintf(stderr, "Cannot set capabilities as user: %s.\n", strerror(errno)); 
+		} else {
+			fprintf(stderr, "Cannot set capabilities as root: %s.\n", strerror(errno));
+		}
+		return -3;
+	}
+
+	if (cap_count > 1) {
+		if (prctl(PR_SET_KEEPCAPS, 1L)) {
+			fprintf(stderr, "Cannot keep capabilities after dropping privileges: %s.\n", strerror(errno));
+			return -4;
+		}
+		if (cap_clear(cap_struct)) {
+			fprintf(stderr, "Cannot clear capability data structure: %s.\n", strerror(errno));
+			return -5;
+		}
+	}
+}
+
+int main(int argc, char **argv, char **envp) {
+	cap_t cap_struct = cap_init();
+	cap_value_t root_caps[2] = { CAP_NET_RAW, CAP_SETUID };
+	cap_value_t user_caps[1] = { CAP_NET_RAW };
+	uid_t user = getuid();
+	int res;
+
+	if (setresuid(0, 0, 0)) {
+		fprintf(stderr, "Cannot switch to root: %s.\n", strerror(errno));
+		return 1;
+	}
+
+	if (res = set_caps(cap_struct, root_caps, sizeof(root_caps)))
+		return res;
+
+	if (setresuid(user, user, user)) {
+		fprintf(stderr, "Cannot drop root privileges: %s.\n", strerror(errno));
+		return 2;
+	}
+
+	if (res = set_caps(cap_struct, user_caps, sizeof(user_caps)))
+		return res;
+
+	if (execve(argv[1], argv + 1, envp)) {
+		fprintf(stderr, "Failed to execute %s: %s\n", argv[1], strerror(errno));
+		return 3;
+	}
+}