From ce268825539ebb94ed9755b9e78480abd863ece1 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 16 May 2018 21:50:35 -0400
Subject: [PATCH] process-util: also filter non-printable characters in
 get_process_com()

We already do that in get_process_cmdline(), which is very similar in
behaviour otherwise. Hence, let's be safe and also filter them in
get_process_comm(). Let's try to retain as much information as we can
though and escape rather than suppress unprintable characters. Let's not
increase comm names beyond the kernel limit on such names however.

Also see discussion about this here:

https://marc.info/?l=linux-api&m=152649570404881&w=2
---
 src/basic/process-util.c     | 19 +++++++++++++++----
 src/test/test-process-util.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index 058f077de06..e3be7b97933 100644
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -76,20 +76,31 @@ int get_process_state(pid_t pid) {
         return (unsigned char) state;
 }
 
-int get_process_comm(pid_t pid, char **name) {
+int get_process_comm(pid_t pid, char **ret) {
+        _cleanup_free_ char *escaped = NULL, *comm = NULL;
         const char *p;
         int r;
 
-        assert(name);
+        assert(ret);
         assert(pid >= 0);
 
+        escaped = new(char, TASK_COMM_LEN);
+        if (!escaped)
+                return -ENOMEM;
+
         p = procfs_file_alloca(pid, "comm");
 
-        r = read_one_line_file(p, name);
+        r = read_one_line_file(p, &comm);
         if (r == -ENOENT)
                 return -ESRCH;
+        if (r < 0)
+                return r;
 
-        return r;
+        /* Escape unprintable characters, just in case, but don't grow the string beyond the underlying size */
+        cellescape(escaped, TASK_COMM_LEN, comm);
+
+        *ret = TAKE_PTR(escaped);
+        return 0;
 }
 
 int get_process_cmdline(pid_t pid, size_t max_length, bool comm_fallback, char **line) {
diff --git a/src/test/test-process-util.c b/src/test/test-process-util.c
index 8b975ff9888..ef18cff70d4 100644
--- a/src/test/test-process-util.c
+++ b/src/test/test-process-util.c
@@ -91,6 +91,38 @@ static void test_get_process_comm(pid_t pid) {
         log_info("PID"PID_FMT" $PATH: '%s'", pid, strna(i));
 }
 
+static void test_get_process_comm_escape_one(const char *input, const char *output) {
+        _cleanup_free_ char *n = NULL;
+
+        log_info("input: <%s> — output: <%s>", input, output);
+
+        assert_se(prctl(PR_SET_NAME, input) >= 0);
+        assert_se(get_process_comm(0, &n) >= 0);
+
+        log_info("got: <%s>", n);
+
+        assert_se(streq_ptr(n, output));
+}
+
+static void test_get_process_comm_escape(void) {
+        _cleanup_free_ char *saved = NULL;
+
+        assert_se(get_process_comm(0, &saved) >= 0);
+
+        test_get_process_comm_escape_one("", "");
+        test_get_process_comm_escape_one("foo", "foo");
+        test_get_process_comm_escape_one("012345678901234", "012345678901234");
+        test_get_process_comm_escape_one("0123456789012345", "012345678901234");
+        test_get_process_comm_escape_one("äöüß", "\\303\\244\\303…");
+        test_get_process_comm_escape_one("xäöüß", "x\\303\\244…");
+        test_get_process_comm_escape_one("xxäöüß", "xx\\303\\244…");
+        test_get_process_comm_escape_one("xxxäöüß", "xxx\\303\\244…");
+        test_get_process_comm_escape_one("xxxxäöüß", "xxxx\\303\\244…");
+        test_get_process_comm_escape_one("xxxxxäöüß", "xxxxx\\303…");
+
+        assert_se(prctl(PR_SET_NAME, saved) >= 0);
+}
+
 static void test_pid_is_unwaited(void) {
         pid_t pid;
 
@@ -572,6 +604,7 @@ int main(int argc, char *argv[]) {
                 test_get_process_comm(getpid());
         }
 
+        test_get_process_comm_escape();
         test_pid_is_unwaited();
         test_pid_is_alive();
         test_personality();
-- 
2.47.3