[PATCH] trace-cmd: Add option to execute traced process as given user

[tz.stoyanov@gmail.com]

From: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>

A new trace-cmd record option is added: "--user". When it is set with
combination of option -F, the traced process is executed in the context
of the specified user.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Suggested-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
[
  Should be applied on top of patch "trace-cmd: Save the tracee memory map
into the trace.dat file."
]

 Documentation/trace-cmd-record.1.txt |  4 +++
 tracecmd/trace-record.c              | 38 +++++++++++++++++++++++++---
 tracecmd/trace-usage.c               |  1 +
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/Documentation/trace-cmd-record.1.txt b/Documentation/trace-cmd-record.1.txt
index 4a59de9..df92354 100644
--- a/Documentation/trace-cmd-record.1.txt
+++ b/Documentation/trace-cmd-record.1.txt
@@ -122,6 +122,10 @@ OPTIONS
 *--mmap*::
      Used with either *-F* or *-P*, save the traced process memory map into
      the trace.dat file.
+
+*--user*::
+     Used with -F, execute the traced process as given user.
+
 *-C* 'clock'::
      Set the trace clock to "clock".
 
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 48081d4..cfaee90 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -33,6 +33,8 @@
 #include <errno.h>
 #include <limits.h>
 #include <libgen.h>
+#include <pwd.h>
+#include <grp.h>
 
 #include "version.h"
 #include "trace-local.h"
@@ -208,6 +210,7 @@ struct common_record_context {
 	struct buffer_instance *instance;
 	const char *output;
 	char *date2ts;
+	char *user;
 	int data_flags;
 
 	int record_all;
@@ -1417,7 +1420,26 @@ static void trace_or_sleep(enum trace_type type)
 		sleep(10);
 }
 
-static void run_cmd(enum trace_type type, int argc, char **argv)
+static void change_user(char *user)
+{
+	struct passwd *pwd;
+
+	if (!user)
+		return;
+
+	pwd = getpwnam(user);
+	if (pwd) {
+		initgroups(user, pwd->pw_gid);
+		setgid(pwd->pw_gid);
+		setuid(pwd->pw_uid);
+
+		setenv("HOME", pwd->pw_dir, 1);
+		setenv("USER", pwd->pw_name, 1);
+		setenv("LOGNAME", pwd->pw_name, 1);
+	}
+}
+
+static void run_cmd(enum trace_type type, char *user, int argc, char **argv)
 {
 	int status;
 	int pid;
@@ -1438,6 +1460,9 @@ static void run_cmd(enum trace_type type, int argc, char **argv)
 			dup2(save_stdout, 1);
 			close(save_stdout);
 		}
+
+		change_user(user);
+
 		if (execvp(argv[0], argv)) {
 			fprintf(stderr, "\n********************\n");
 			fprintf(stderr, " Unable to exec %s\n", argv[0]);
@@ -4548,6 +4573,7 @@ void update_first_instance(struct buffer_instance *instance, int topt)
 }
 
 enum {
+	OPT_user		= 243,
 	OPT_mmap		= 244,
 	OPT_quiet		= 245,
 	OPT_debug		= 246,
@@ -4780,6 +4806,7 @@ static void parse_record_options(int argc,
 			{"quiet", no_argument, NULL, OPT_quiet},
 			{"help", no_argument, NULL, '?'},
 			{"mmap", no_argument, NULL, OPT_mmap},
+			{"user", required_argument, NULL, OPT_user},
 			{"module", required_argument, NULL, OPT_module},
 			{NULL, 0, NULL, 0}
 		};
@@ -5011,6 +5038,9 @@ static void parse_record_options(int argc,
 		case 'i':
 			ignore_event_not_found = 1;
 			break;
+		case OPT_user:
+			ctx->user = strdup(optarg);
+			break;
 		case OPT_mmap:
 			get_mmap = 1;
 			break;
@@ -5079,7 +5109,9 @@ static void parse_record_options(int argc,
 	if (!ctx->filtered && ctx->instance->filter_mod)
 		add_func(&ctx->instance->filter_funcs,
 			 ctx->instance->filter_mod, "*");
-
+	if (ctx->user && !filter_task)
+		warning("--user %s is ignored, no traced process is specified",
+			ctx->user);
 	if (filter_task && get_mmap)
 		do_ptrace = 1;
 
@@ -5237,7 +5269,7 @@ static void record_trace(int argc, char **argv,
 	}
 
 	if (ctx->run_command)
-		run_cmd(type, (argc - optind) - 1, &argv[optind + 1]);
+		run_cmd(type, ctx->user, (argc - optind) - 1, &argv[optind + 1]);
 	else {
 		update_task_filter();
 		tracecmd_enable_tracing();
diff --git a/tracecmd/trace-usage.c b/tracecmd/trace-usage.c
index c658ede..fcc314e 100644
--- a/tracecmd/trace-usage.c
+++ b/tracecmd/trace-usage.c
@@ -58,6 +58,7 @@ static struct usage_help usage_help[] = {
 		"          --max-graph-depth limit function_graph depth\n"
 		"          --no-filter include trace-cmd threads in the trace\n"
 		"          --mmap used with -F or -P, save the traced process memory map into the trace.dat file\n"
+		"          --user used with -F, execute the traced process as given user\n"
 	},
 	{
 		"start",
-- 
2.21.0