From: Karel Zak <kzak@redhat.com>
Date: Thu, 22 Jul 2021 09:03:54 +0000 (+0200)
Subject: lslogins: use sd_journal_get_data() in proper way
X-Git-Tag: v2.37.1~9
X-Git-Url: http://git.ipfire.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=f6261700621d66fb252e3e01756190d8772dd1a8;p=thirdparty%2Futil-linux.git

lslogins: use sd_journal_get_data() in proper way

man sd_journal_get_data:
    The returned data is in a read-only memory map and is only valid until the next invocation
    of sd_journal_get_data().

It means that use data after 3x sd_journal_get_data() is really bad
idea. It also seems better to not assume the fields are zero
terminated as journal API works with void* and size_t to address the
data.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1984704
Signed-off-by: Karel Zak <kzak@redhat.com>
---

diff --git a/login-utils/lslogins.c b/login-utils/lslogins.c
index 908d78b11a..cf1b8e7caf 100644
--- a/login-utils/lslogins.c
+++ b/login-utils/lslogins.c
@@ -1231,14 +1231,28 @@ static void fill_table(const void *u, const VISIT which, const int depth __attri
 	}
 }
 #ifdef HAVE_LIBSYSTEMD
+static char *get_journal_data(sd_journal *j, const char *name)
+{
+	const char *data = NULL, *p;
+	size_t len = 0;
+
+	if (sd_journal_get_data(j, name, (const void **) &data, &len) < 0
+	    || !data || !len)
+		return NULL;
+
+	/* Get rid of journal entry field identifiers */
+	p = strnchr(data, len, '=');
+	if (!p || !*(p + 1))
+		return NULL;
+	p++;
+
+	return xstrndup(p, len - (p - data));
+}
+
 static void print_journal_tail(const char *journal_path, uid_t uid, size_t len, int time_mode)
 {
 	sd_journal *j;
-	char *match, *timestamp;
-	uint64_t x;
-	time_t t;
-	const char *identifier, *pid, *message;
-	size_t identifier_len, pid_len, message_len;
+	char *match;
 
 	if (journal_path)
 		sd_journal_open_directory(&j, journal_path, 0);
@@ -1252,30 +1266,27 @@ static void print_journal_tail(const char *journal_path, uid_t uid, size_t len,
 	sd_journal_previous_skip(j, len);
 
 	do {
-		if (0 > sd_journal_get_data(j, "SYSLOG_IDENTIFIER",
-				(const void **) &identifier, &identifier_len))
-			goto done;
-		if (0 > sd_journal_get_data(j, "_PID",
-				(const void **) &pid, &pid_len))
-			goto done;
-		if (0 > sd_journal_get_data(j, "MESSAGE",
-				(const void **) &message, &message_len))
-			goto done;
+		char *id, *pid, *msg, *ts;
+		uint64_t x;
+		time_t t;
 
 		sd_journal_get_realtime_usec(j, &x);
 		t = x / 1000000;
-		timestamp = make_time(time_mode, t);
-		/* Get rid of journal entry field identifiers */
-		identifier = strchr(identifier, '=') + 1;
-		pid = strchr(pid, '=') + 1;
-		message = strchr(message, '=') + 1;
-
-		fprintf(stdout, "%s %s[%s]: %s\n", timestamp, identifier, pid,
-			message);
-		free(timestamp);
+		ts = make_time(time_mode, t);
+
+		id = get_journal_data(j, "SYSLOG_IDENTIFIER");
+		pid = get_journal_data(j, "_PID");
+		msg = get_journal_data(j, "MESSAGE");
+
+		if (ts && id && pid && msg)
+			fprintf(stdout, "%s %s[%s]: %s\n", ts, id, pid, msg);
+
+		free(ts);
+		free(id);
+		free(pid);
+		free(msg);
 	} while (sd_journal_next(j));
 
-done:
 	free(match);
 	sd_journal_flush_matches(j);
 	sd_journal_close(j);