From c394463688c332199a8fcabe6f84818b57c730b3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Tue, 2 Oct 2018 12:46:31 +0200
Subject: [PATCH] journal-upload: add asserts that snprintf does not return an
 error

LGMT complains:
> The size argument of this snprintf call is derived from its return value,
> which may exceed the size of the buffer and overflow.

Let's make sure that r is non-negative. (This shouldn't occur unless the format
string is borked, so let's just add an assert.)
Then, let's reorder the comparison to avoid the potential overflow.

(cherry picked from commit 91db8ed5b2e67abf738381a6ed6a05a8271498cd)

Resolves: #1694605
---
 src/journal-remote/journal-upload-journal.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/journal-remote/journal-upload-journal.c b/src/journal-remote/journal-upload-journal.c
index 5fd639a76a..c244a76932 100644
--- a/src/journal-remote/journal-upload-journal.c
+++ b/src/journal-remote/journal-upload-journal.c
@@ -30,7 +30,8 @@ static ssize_t write_entry(char *buf, size_t size, Uploader *u) {
 
                         r = snprintf(buf + pos, size - pos,
                                      "__CURSOR=%s\n", u->current_cursor);
-                        if (pos + r > size)
+                        assert(r >= 0);
+                        if ((size_t) r > size - pos)
                                 /* not enough space */
                                 return pos;
 
@@ -54,7 +55,8 @@ static ssize_t write_entry(char *buf, size_t size, Uploader *u) {
 
                         r = snprintf(buf + pos, size - pos,
                                      "__REALTIME_TIMESTAMP="USEC_FMT"\n", realtime);
-                        if (r + pos > size)
+                        assert(r >= 0);
+                        if ((size_t) r > size - pos)
                                 /* not enough space */
                                 return pos;
 
@@ -79,7 +81,8 @@ static ssize_t write_entry(char *buf, size_t size, Uploader *u) {
 
                         r = snprintf(buf + pos, size - pos,
                                      "__MONOTONIC_TIMESTAMP="USEC_FMT"\n", monotonic);
-                        if (r + pos > size)
+                        assert(r >= 0);
+                        if ((size_t) r > size - pos)
                                 /* not enough space */
                                 return pos;
 
@@ -104,7 +107,8 @@ static ssize_t write_entry(char *buf, size_t size, Uploader *u) {
 
                         r = snprintf(buf + pos, size - pos,
                                      "_BOOT_ID=%s\n", sd_id128_to_string(boot_id, sid));
-                        if (r + pos > size)
+                        assert(r >= 0);
+                        if ((size_t) r > size - pos)
                                 /* not enough space */
                                 return pos;