core: when deserializing state always use read_line(…, LONG_LINE_MAX, …)

This should be much better than fgets(), as we can read substantially
longer lines and overly long lines result in proper errors.

Fixes a vulnerability discovered by Jann Horn at Google.

CVE-2018-15686
LP: #1796402
https://bugzilla.redhat.com/show_bug.cgi?id=1639071

(cherry picked from commit 8948b3415d762245ebf5e19d80b97d4d8cc208c1)

Resolves: CVE-2018-15686

4 files changed, 50 insertions, 52 deletions

diff --git a/src/core/job.c b/src/core/job.c
index 734756b666..8552ffb704 100644
--- a/src/core/job.c
+++ b/src/core/job.c
@@ -10,6 +10,7 @@
 #include "dbus-job.h"
 #include "dbus.h"
 #include "escape.h"
+#include "fileio.h"
 #include "job.h"
 #include "log.h"
 #include "macro.h"
@@ -1091,24 +1092,26 @@ int job_serialize(Job *j, FILE *f) {
 }
 
 int job_deserialize(Job *j, FILE *f) {
+        int r;
+
         assert(j);
         assert(f);
 
         for (;;) {
-                char line[LINE_MAX], *l, *v;
+                _cleanup_free_ char *line = NULL;
+                char *l, *v;
                 size_t k;
 
-                if (!fgets(line, sizeof(line), f)) {
-                        if (feof(f))
-                                return 0;
-                        return -errno;
-                }
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to read serialization line: %m");
+                if (r == 0)
+                        return 0;
 
-                char_array_0(line);
                 l = strstrip(line);
 
                 /* End marker */
-                if (l[0] == 0)
+                if (isempty(l))
                         return 0;
 
                 k = strcspn(l, "=");
diff --git a/src/core/manager.c b/src/core/manager.c
index 3b2fe11e87..c83e296cf3 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -3144,22 +3144,17 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
         m->n_reloading++;
 
         for (;;) {
-                char line[LINE_MAX];
+                _cleanup_free_ char *line = NULL;
                 const char *val, *l;
 
-                if (!fgets(line, sizeof(line), f)) {
-                        if (feof(f))
-                                r = 0;
-                        else
-                                r = -errno;
-
-                        goto finish;
-                }
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to read serialization line: %m");
+                if (r == 0)
+                        break;
 
-                char_array_0(line);
                 l = strstrip(line);
-
-                if (l[0] == 0)
+                if (isempty(l)) /* end marker */
                         break;
 
                 if ((val = startswith(l, "current-job-id="))) {
@@ -3326,29 +3321,27 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
         }
 
         for (;;) {
-                Unit *u;
-                char name[UNIT_NAME_MAX+2];
+                _cleanup_free_ char *line = NULL;
                 const char* unit_name;
+                Unit *u;
 
                 /* Start marker */
-                if (!fgets(name, sizeof(name), f)) {
-                        if (feof(f))
-                                r = 0;
-                        else
-                                r = -errno;
-
-                        goto finish;
-                }
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to read serialization line: %m");
+                if (r == 0)
+                        break;
 
-                char_array_0(name);
-                unit_name = strstrip(name);
+                unit_name = strstrip(line);
 
                 r = manager_load_unit(m, unit_name, NULL, NULL, &u);
                 if (r < 0) {
                         log_notice_errno(r, "Failed to load unit \"%s\", skipping deserialization: %m", unit_name);
-                        if (r == -ENOMEM)
-                                goto finish;
-                        unit_deserialize_skip(f);
+
+                        r = unit_deserialize_skip(f);
+                        if (r < 0)
+                                return r;
+
                         continue;
                 }
 
diff --git a/src/core/unit.c b/src/core/unit.c
index 721d8d60a3..cc43ddc4f1 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -3368,21 +3368,19 @@ int unit_deserialize(Unit *u, FILE *f, FDSet *fds) {
         assert(fds);
 
         for (;;) {
-                char line[LINE_MAX], *l, *v;
+                _cleanup_free_ char *line = NULL;
                 CGroupIPAccountingMetric m;
+                char *l, *v;
                 size_t k;
 
-                if (!fgets(line, sizeof(line), f)) {
-                        if (feof(f))
-                                return 0;
-                        return -errno;
-                }
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to read serialization line: %m");
+                if (r == 0) /* eof */
+                        break;
 
-                char_array_0(line);
                 l = strstrip(line);
-
-                /* End marker */
-                if (isempty(l))
+                if (isempty(l)) /* End marker */
                         break;
 
                 k = strcspn(l, "=");
@@ -3657,23 +3655,27 @@ int unit_deserialize(Unit *u, FILE *f, FDSet *fds) {
         return 0;
 }
 
-void unit_deserialize_skip(FILE *f) {
+int unit_deserialize_skip(FILE *f) {
+        int r;
         assert(f);
 
         /* Skip serialized data for this unit. We don't know what it is. */
 
         for (;;) {
-                char line[LINE_MAX], *l;
+                _cleanup_free_ char *line = NULL;
+                char *l;
 
-                if (!fgets(line, sizeof line, f))
-                        return;
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to read serialization line: %m");
+                if (r == 0)
+                        return 0;
 
-                char_array_0(line);
                 l = strstrip(line);
 
                 /* End marker */
                 if (isempty(l))
-                        return;
+                        return 1;
         }
 }
 
diff --git a/src/core/unit.h b/src/core/unit.h
index b3131eba1b..e1a60da244 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -679,7 +679,7 @@ bool unit_can_serialize(Unit *u) _pure_;
 
 int unit_serialize(Unit *u, FILE *f, FDSet *fds, bool serialize_jobs);
 int unit_deserialize(Unit *u, FILE *f, FDSet *fds);
-void unit_deserialize_skip(FILE *f);
+int unit_deserialize_skip(FILE *f);
 
 int unit_serialize_item(Unit *u, FILE *f, const char *key, const char *value);
 int unit_serialize_item_escaped(Unit *u, FILE *f, const char *key, const char *value);