From 8c8f08304ecacc9d714ce8293ff8b4495d8c820c Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Wed, 1 May 2024 13:57:41 +0100
Subject: [PATCH 1/2] gdocumentportal: Factor out opening_ro_might_succeed()

No functional change.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 gio/gdocumentportal.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/gio/gdocumentportal.c b/gio/gdocumentportal.c
index 382e2aab6..531156660 100644
--- a/gio/gdocumentportal.c
+++ b/gio/gdocumentportal.c
@@ -90,6 +90,24 @@ enum {
   XDP_ADD_FLAGS_FLAGS_ALL                  = ((1 << 3) - 1)
 };
 
+/*
+ * Assume that opening a file read/write failed with @saved_errno,
+ * and return TRUE if opening the same file read-only might succeed.
+ */
+static gboolean
+opening_ro_might_succeed (int saved_errno)
+{
+  switch (saved_errno)
+    {
+    case EACCES:
+    case EISDIR:
+      return TRUE;
+
+    default:
+      return FALSE;
+    }
+}
+
 GList *
 g_document_portal_add_documents (GList       *uris,
                                  const char  *app_id,
@@ -131,7 +149,7 @@ g_document_portal_add_documents (GList       *uris,
           int fd;
 
           fd = g_open (path, O_CLOEXEC | O_RDWR);
-          if (fd == -1 && (errno == EACCES || errno == EISDIR))
+          if (fd == -1 && opening_ro_might_succeed (errno))
             {
               /* If we don't have write access, fall back to read-only,
                * and stop requesting the write permission */

From a869dcb90b66bf6aac7e58753f3a5bb80bd3666c Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Wed, 1 May 2024 14:08:58 +0100
Subject: [PATCH 2/2] gdocumentportal: Treat more error codes as a permissions
 error

If the file to be added is on a read-only filesystem, opening read/write
will fail with EROFS. In this case we should fall back to opening it
read-only, the same way we already do if write access is forbidden by
DAC or MAC.

An easy way to reproduce this test failure is to build and test GLib
in a podman container, with its source code read-only and its build
directory read/write:

    podman run --rm -it \
    -v $(pwd):$(pwd):ro \
    -v $(pwd)/_build:$(pwd)/_build:rw \
    -w $(pwd) ...

Before this commit, the dbus-appinfo test would fail, because opening
${srcdir}/gio/tests/org.gtk.test.dbusappinfo.flatpak.desktop read/write
would fail with EROFS.

For completeness, give similar handling to the other error codes
documented in Linux open(2) that might succeed if re-attempted using
read-only access: according to that documentation, we could get EPERM
if opening read/write is prevented by fcntl F_ADD_SEALS, or ETXTBSY
if the file is an executable that is currently being run.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 gio/gdocumentportal.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gio/gdocumentportal.c b/gio/gdocumentportal.c
index 531156660..0b55c3ef9 100644
--- a/gio/gdocumentportal.c
+++ b/gio/gdocumentportal.c
@@ -101,6 +101,15 @@ opening_ro_might_succeed (int saved_errno)
     {
     case EACCES:
     case EISDIR:
+#ifdef EPERM
+    case EPERM:
+#endif
+#ifdef EROFS
+    case EROFS:
+#endif
+#ifdef ETXTBSY
+    case ETXTBSY:
+#endif
       return TRUE;
 
     default: