Change in libosmocore[master]: exec: Introduce osmo_system_nowait2() to allow specify a user

[laforge]

laforge has uploaded this change for review. ( https://gerrit.osmocom.org/c/libosmocore/+/17852 )


Change subject: exec: Introduce osmo_system_nowait2() to allow specify a user
......................................................................

exec: Introduce osmo_system_nowait2() to allow specify a user

For a process running as root, it may be desirable to drop privileges
down to a normal user  before executing an external command.  Let's
add a new API function for that.

Change-Id: If1431f930f72a8d6c1d102426874a11b7a2debd9
---
M include/osmocom/core/exec.h
M src/exec.c
2 files changed, 28 insertions(+), 1 deletion(-)



  git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/52/17852/1

diff --git a/include/osmocom/core/exec.h b/include/osmocom/core/exec.h
index 6bbd352..e63ec11 100644
--- a/include/osmocom/core/exec.h
+++ b/include/osmocom/core/exec.h
@@ -25,4 +25,5 @@
 int osmo_environment_filter(char **out, size_t out_len, char **in, const char **whitelist);
 int osmo_environment_append(char **out, size_t out_len, char **in);
 int osmo_close_all_fds_above(int last_fd_to_keep);
+int osmo_system_nowait2(const char *command, const char **env_whitelist, char **addl_env, const char *user);
 int osmo_system_nowait(const char *command, const char **env_whitelist, char **addl_env);
diff --git a/src/exec.c b/src/exec.c
index 62f5919..dfe019b 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -23,6 +23,7 @@
 #include "config.h"
 #ifndef EMBEDDED
 
+#define _GNU_SOURCE
 #include <unistd.h>
 
 #include <errno.h>
@@ -31,6 +32,7 @@
 #include <stdio.h>
 #include <dirent.h>
 #include <sys/types.h>
+#include <pwd.h>
 
 #include <osmocom/core/logging.h>
 #include <osmocom/core/utils.h>
@@ -203,12 +205,20 @@
  *  \param[in] command the shell command to be executed, see system(3)
  *  \param[in] env_whitelist A white-list of keys for environment variables
  *  \param[in] addl_env any additional environment variables to be appended
+ *  \param[in] user name of the user to which we should switch before executing the command
  *  \returns PID of generated child process; negative on error
  */
-int osmo_system_nowait(const char *command, const char **env_whitelist, char **addl_env)
+int osmo_system_nowait2(const char *command, const char **env_whitelist, char **addl_env, const char *user)
 {
+	struct passwd *pw = NULL;
 	int rc;
 
+	if (user) {
+		pw = getpwnam(user);
+		if (!pw)
+			return -EINVAL;
+	}
+
 	rc = fork();
 	if (rc == 0) {
 		/* we are in the child */
@@ -232,6 +242,16 @@
 				return rc;
 		}
 
+		/* drop privileges */
+		if (pw) {
+			if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
+				exit(1);
+
+			if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
+				exit(1);
+
+		}
+
 		/* if we want to behave like system(3), we must go via the shell */
 		execle("/bin/sh", "sh", "-c", command, (char *) NULL, new_env);
 		/* only reached in case of error */
@@ -244,4 +264,10 @@
 	}
 }
 
+int osmo_system_nowait(const char *command, const char **env_whitelist, char **addl_env)
+{
+	return osmo_system_nowait2(command, env_whitelist, addl_env, NULL);
+}
+
+
 #endif /* EMBEDDED */

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Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: If1431f930f72a8d6c1d102426874a11b7a2debd9
Gerrit-Change-Number: 17852
Gerrit-PatchSet: 1
Gerrit-Owner: laforge <laforge at osmocom.org>
Gerrit-MessageType: newchange
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