From 5cd12abaa0c0f3a06c9ff2048941fbe6e8b3577e Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 6 Aug 2020 17:00:07 +0200
Subject: [PATCH] user-record: deal with invalid GECOS fields gracefully

Let's fix up invalid GECOS fields both when we convert from NSS to JSON
and the other way round.

Kinda sucks we have to do that, but NSS does it when writing data to
/etc/passwd, so let's do the same.

Fixes: #16668
---
 src/shared/user-record-nss.c | 24 ++++++++++++++++++++----
 src/shared/user-record.c     | 19 +++++++++++++------
 2 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/src/shared/user-record-nss.c b/src/shared/user-record-nss.c
index f265a2af93..b27a12c55d 100644
--- a/src/shared/user-record-nss.c
+++ b/src/shared/user-record-nss.c
@@ -5,6 +5,7 @@
 #include "libcrypt-util.h"
 #include "strv.h"
 #include "user-record-nss.h"
+#include "user-util.h"
 
 #define SET_IF(field, condition, value, fallback)  \
         field = (condition) ? (value) : (fallback)
@@ -34,10 +35,25 @@ int nss_passwd_to_user_record(
         if (r < 0)
                 return r;
 
-        r = free_and_strdup(&hr->real_name,
-                            streq_ptr(pwd->pw_gecos, hr->user_name) ? NULL : empty_to_null(pwd->pw_gecos));
-        if (r < 0)
-                return r;
+        /* Some bad NSS modules synthesize GECOS fields with embedded ":" or "\n" characters, which are not
+         * something we can output in /etc/passwd compatible format, since these are record separators
+         * there. We normally refuse that, but we need to maintain compatibility with arbitrary NSS modules,
+         * hence let's do what glibc does: mangle the data to fit the format. */
+        if (isempty(pwd->pw_gecos) || streq_ptr(pwd->pw_gecos, hr->user_name))
+                hr->real_name = mfree(hr->real_name);
+        else if (valid_gecos(pwd->pw_gecos)) {
+                r = free_and_strdup(&hr->real_name, pwd->pw_gecos);
+                if (r < 0)
+                        return r;
+        } else {
+                _cleanup_free_ char *mangled = NULL;
+
+                mangled = mangle_gecos(pwd->pw_gecos);
+                if (!mangled)
+                        return -ENOMEM;
+
+                free_and_replace(hr->real_name, mangled);
+        }
 
         r = free_and_strdup(&hr->home_directory, empty_to_null(pwd->pw_dir));
         if (r < 0)
diff --git a/src/shared/user-record.c b/src/shared/user-record.c
index 16edaa45fa..2c0de383e0 100644
--- a/src/shared/user-record.c
+++ b/src/shared/user-record.c
@@ -206,7 +206,6 @@ int json_dispatch_realm(const char *name, JsonVariant *variant, JsonDispatchFlag
 static int json_dispatch_gecos(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata) {
         char **s = userdata;
         const char *n;
-        int r;
 
         if (json_variant_is_null(variant)) {
                 *s = mfree(*s);
@@ -217,12 +216,20 @@ static int json_dispatch_gecos(const char *name, JsonVariant *variant, JsonDispa
                 return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not a string.", strna(name));
 
         n = json_variant_string(variant);
-        if (!valid_gecos(n))
-                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not a valid GECOS compatible real name.", strna(name));
+        if (valid_gecos(n)) {
+                if (free_and_strdup(s, n) < 0)
+                        return json_log_oom(variant, flags);
+        } else {
+                _cleanup_free_ char *m = NULL;
 
-        r = free_and_strdup(s, n);
-        if (r < 0)
-                return json_log(variant, flags, r, "Failed to allocate string: %m");
+                json_log(variant, flags|JSON_DEBUG, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not a valid GECOS compatible string, mangling.", strna(name));
+
+                m = mangle_gecos(n);
+                if (!m)
+                        return json_log_oom(variant, flags);
+
+                free_and_replace(*s, m);
+        }
 
         return 0;
 }