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From cb6fce9e4122ace2960c437def3b1a197bb49b3a Mon Sep 17 00:00:00 2001
From: Ryan Gonzalez <rymg19@gmail.com>
Date: Tue, 2 Mar 2021 13:20:07 -0600
Subject: [PATCH 1/3] Disallow @@ and @@u usage in desktop files

Fixes #4146.
---
 common/flatpak-dir.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/common/flatpak-dir.c b/common/flatpak-dir.c
index e6e4d6fb3..7d3374dad 100644
--- a/common/flatpak-dir.c
+++ b/common/flatpak-dir.c
@@ -7139,6 +7139,8 @@ export_desktop_file (const char         *app,
                 g_string_append_printf (new_exec, " @@ %s @@", arg);
               else if (strcasecmp (arg, "%u") == 0)
                 g_string_append_printf (new_exec, " @@u %s @@", arg);
+              else if (strcmp (arg, "@@") == 0 || strcmp (arg, "@@u") == 0)
+                g_print (_("Skipping invalid Exec argument %s\n"), arg);
               else
                 g_string_append_printf (new_exec, " %s", arg);
             }

From 0bdcb88b2d0013aa435dc03950fb42cef2cbd359 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Fri, 5 Mar 2021 13:49:36 +0000
Subject: [PATCH 2/3] dir: Reserve the whole @@ prefix

If we add new features analogous to file forwarding later, we might
find that we need a different magic token. Let's reserve the whole
@@* namespace so we can call it @@something-else.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 common/flatpak-dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/common/flatpak-dir.c b/common/flatpak-dir.c
index 7d3374dad..facfab37a 100644
--- a/common/flatpak-dir.c
+++ b/common/flatpak-dir.c
@@ -7139,7 +7139,7 @@ export_desktop_file (const char         *app,
                 g_string_append_printf (new_exec, " @@ %s @@", arg);
               else if (strcasecmp (arg, "%u") == 0)
                 g_string_append_printf (new_exec, " @@u %s @@", arg);
-              else if (strcmp (arg, "@@") == 0 || strcmp (arg, "@@u") == 0)
+              else if (g_str_has_prefix (arg, "@@"))
                 g_print (_("Skipping invalid Exec argument %s\n"), arg);
               else
                 g_string_append_printf (new_exec, " %s", arg);

From 230f4c3521cd0dffa446ab9b70e958cdd9241bbe Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Fri, 5 Mar 2021 13:51:33 +0000
Subject: [PATCH 3/3] dir: Refuse to export .desktop files with suspicious uses
 of @@ tokens

This is either a malicious/compromised app trying to do an attack, or
a mistake that will break handling of %f, %u and so on. Either way,
if we refuse to export the .desktop file, resulting in installation
failing, then it makes the rejection more obvious than quietly
removing the magic tokens.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 common/flatpak-dir.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/common/flatpak-dir.c b/common/flatpak-dir.c
index facfab37a..c5edf346f 100644
--- a/common/flatpak-dir.c
+++ b/common/flatpak-dir.c
@@ -7140,7 +7140,11 @@ export_desktop_file (const char         *app,
               else if (strcasecmp (arg, "%u") == 0)
                 g_string_append_printf (new_exec, " @@u %s @@", arg);
               else if (g_str_has_prefix (arg, "@@"))
-                g_print (_("Skipping invalid Exec argument %s\n"), arg);
+                {
+                  flatpak_fail_error (error, FLATPAK_ERROR_EXPORT_FAILED,
+                                     _("Invalid Exec argument %s"), arg);
+                  goto out;
+                }
               else
                 g_string_append_printf (new_exec, " %s", arg);
             }