[PATCH 1/2] src/vfs: probe O_TMPFILE support on the base mount in the idmapped tests

openat_tmpfile_supported() in the idmapped mount tests probes O_TMPFILE
on the idmapped mount (open_tree_fd) as the test's fsuid -- but that
fsuid is not mapped by the idmapped mount under test, so it really asks
"can this unmapped caller create a tmpfile through this idmap?" instead
of "does the filesystem support O_TMPFILE?".

On overlayfs this is a false negative: the backing tmpfile ends up owned
by an unmapped id, overlayfs opens it with O_NOATIME and may_open()
returns -EPERM, so the tmpfile sub-tests are wrongly skipped.

O_TMPFILE support is a property of the filesystem, not of the idmapped
mount or the caller's mapping. Probe info->t_dir1_fd, the base mount
that the caller owns, exactly as the non-idmapped setgid tests already
do. The probe then succeeds on every filesystem and the tmpfile
sub-tests run as the mapped fsuid.

Signed-off-by: Christian Brauner (Amutable) <[email protected]>
---
 src/vfs/idmapped-mounts.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/vfs/idmapped-mounts.c b/src/vfs/idmapped-mounts.c
index ed9992f9..8f8441c9 100644
--- a/src/vfs/idmapped-mounts.c
+++ b/src/vfs/idmapped-mounts.c
@@ -3838,7 +3838,7 @@ int tcore_setgid_create_idmapped(const struct vfstest_info *info)
 		goto out;
 	}
 
-	supported = openat_tmpfile_supported(open_tree_fd);
+	supported = openat_tmpfile_supported(info->t_dir1_fd);
 
 	pid = fork();
 	if (pid < 0) {
@@ -4014,7 +4014,7 @@ int tcore_setgid_create_idmapped_in_userns(const struct vfstest_info *info)
 		goto out;
 	}
 
-	supported = openat_tmpfile_supported(open_tree_fd);
+	supported = openat_tmpfile_supported(info->t_dir1_fd);
 
 	pid = fork();
 	if (pid < 0) {
@@ -7733,7 +7733,7 @@ static int setgid_create_umask_idmapped(const struct vfstest_info *info)
 		goto out;
 	}
 
-	supported = openat_tmpfile_supported(open_tree_fd);
+	supported = openat_tmpfile_supported(info->t_dir1_fd);
 
 	pid = fork();
 	if (pid < 0) {
@@ -7947,7 +7947,7 @@ static int setgid_create_umask_idmapped_in_userns(const struct vfstest_info *inf
 		goto out;
 	}
 
-	supported = openat_tmpfile_supported(open_tree_fd);
+	supported = openat_tmpfile_supported(info->t_dir1_fd);
 
 	/*
 	 * Below we verify that setgid inheritance for a newly created file or
@@ -8181,7 +8181,7 @@ static int setgid_create_acl_idmapped(const struct vfstest_info *info)
 		goto out;
 	}
 
-	supported = openat_tmpfile_supported(open_tree_fd);
+	supported = openat_tmpfile_supported(info->t_dir1_fd);
 
 	pid = fork();
 	if (pid < 0) {
@@ -8536,7 +8536,7 @@ static int setgid_create_acl_idmapped_in_userns(const struct vfstest_info *info)
 		goto out;
 	}
 
-	supported = openat_tmpfile_supported(open_tree_fd);
+	supported = openat_tmpfile_supported(info->t_dir1_fd);
 
 	/*
 	 * Below we verify that setgid inheritance for a newly created file or

-- 
2.47.3