Commit 78ff640819 ("vfs: Convert tracefs to use the new mount API")
converted tracefs to use the new mount APIs caused mount options
(e.g. gid=<gid>) to not take effect.
The tracefs superblock can be updated from multiple paths:
- on fs_initcall() to init_trace_printk_function_export()
- from a work queue to initialize eventfs
tracer_init_tracefs_work_func()
- fsconfig() syscall to mount or remount of tracefs
The tracefs superblock root inode gets created early on in
init_trace_printk_function_export().
With the new mount API, tracefs effectively uses get_tree_single() instead
of the old API mount_single().
Previously, mount_single() ensured that the options are always applied to
the superblock root inode:
(1) If the root inode didn't exist, call fill_super() to create it
and apply the options.
(2) If the root inode exists, call reconfigure_single() which
effectively calls tracefs_apply_options() to parse and apply
options to the subperblock's fs_info and inode and remount
eventfs (if necessary)
On the other hand, get_tree_single() effectively calls vfs_get_super()
which:
(3) If the root inode doesn't exists, calls fill_super() to create it
and apply the options.
(4) If the root inode already exists, updates the fs_context root
with the superblock's root inode.
(4) above is always the case for tracefs mounts, since the super block's
root inode will already be created by init_trace_printk_function_export().
This means that the mount options get ignored:
- Since it isn't applied to the superblock's root inode, it doesn't
get inherited by the children.
- Since eventfs is initialized from a separate work queue and
before call to mount with the options, and it doesn't get remounted
for mount.
Ensure that the mount options are applied to the super block and eventfs
is remounted to respect the mount options.
To understand this better, if fstab has the following:
tracefs /sys/kernel/tracing tracefs nosuid,nodev,noexec,gid=tracing 0 0
On boot up, permissions look like:
# ls -l /sys/kernel/tracing/trace
-rw-r----- 1 root root 0 Nov 1 08:37 /sys/kernel/tracing/trace
When it should look like:
# ls -l /sys/kernel/tracing/trace
-rw-r----- 1 root tracing 0 Nov 1 08:37 /sys/kernel/tracing/trace
Link: https://lore.kernel.org/r/536e99d3-345c-448b-adee-a21389d7ab4b@redhat.com/
Cc: Eric Sandeen <sandeen@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Ali Zahraee <ahzahraee@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 78ff640819 ("vfs: Convert tracefs to use the new mount API")
Link: https://lore.kernel.org/20241030171928.4168869-2-kaleshsingh@google.com
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
e4d32142d1