From: "Steven Rostedt (Google)" rostedt@goodmis.org

The change to update the permissions of the eventfs_inode had the misconception that using the tracefs_inode would find all the eventfs_inodes that have been updated and reset them on remount. The problem with this approach is that the eventfs_inodes are freed when they are no longer used (basically the reason the eventfs system exists). When they are freed, the updated eventfs_inodes are not reset on a remount because their tracefs_inodes have been freed.

Instead, since the events directory eventfs_inode always has a tracefs_inode pointing to it (it is not freed when finished), and the events directory has a link to all its children, have the eventfs_remount() function only operate on the events eventfs_inode and have it descend into its children updating their uid and gids.

Link: https://lore.kernel.org/all/CAK7LNARXgaWw3kH9JgrnH4vK6fr8LDkNKf3wq8NhMWJrVwJ... Link: https://lore.kernel.org/linux-trace-kernel/20240523051539.754424703@goodmis....

Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Andrew Morton akpm@linux-foundation.org Fixes: baa23a8d4360d ("tracefs: Reset permissions on remount if permissions are options") Reported-by: Masahiro Yamada masahiroy@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- fs/tracefs/event_inode.c | 44 ++++++++++++++++++++++++++++------------ 1 file changed, 31 insertions(+), 13 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 5dfb1ccd56ea..129d0f54ba62 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -305,27 +305,27 @@ static const struct file_operations eventfs_file_operations = { .llseek = generic_file_llseek, };

-/* - * On a remount of tracefs, if UID or GID options are set, then - * the mount point inode permissions should be used. - * Reset the saved permission flags appropriately. - */ -void eventfs_remount(struct tracefs_inode *ti, bool update_uid, bool update_gid) +static void eventfs_set_attrs(struct eventfs_inode *ei, bool update_uid, kuid_t uid, + bool update_gid, kgid_t gid, int level) { - struct eventfs_inode *ei = ti->private; + struct eventfs_inode *ei_child;

- if (!ei) + /* Update events/<system>/<event> */ + if (WARN_ON_ONCE(level > 3)) return;

if (update_uid) { ei->attr.mode &= ~EVENTFS_SAVE_UID; - ei->attr.uid = ti->vfs_inode.i_uid; + ei->attr.uid = uid; }

- if (update_gid) { ei->attr.mode &= ~EVENTFS_SAVE_GID; - ei->attr.gid = ti->vfs_inode.i_gid; + ei->attr.gid = gid; + } + + list_for_each_entry(ei_child, &ei->children, list) { + eventfs_set_attrs(ei_child, update_uid, uid, update_gid, gid, level + 1); }

if (!ei->entry_attrs) @@ -334,13 +334,31 @@ void eventfs_remount(struct tracefs_inode *ti, bool update_uid, bool update_gid) for (int i = 0; i < ei->nr_entries; i++) { if (update_uid) { ei->entry_attrs[i].mode &= ~EVENTFS_SAVE_UID; - ei->entry_attrs[i].uid = ti->vfs_inode.i_uid; + ei->entry_attrs[i].uid = uid; } if (update_gid) { ei->entry_attrs[i].mode &= ~EVENTFS_SAVE_GID; - ei->entry_attrs[i].gid = ti->vfs_inode.i_gid; + ei->entry_attrs[i].gid = gid; } } + +} + +/* + * On a remount of tracefs, if UID or GID options are set, then + * the mount point inode permissions should be used. + * Reset the saved permission flags appropriately. + */ +void eventfs_remount(struct tracefs_inode *ti, bool update_uid, bool update_gid) +{ + struct eventfs_inode *ei = ti->private; + + /* Only the events directory does the updates */ + if (!ei || !ei->is_events || ei->is_freed) + return; + + eventfs_set_attrs(ei, update_uid, ti->vfs_inode.i_uid, + update_gid, ti->vfs_inode.i_gid, 0); }

/* Return the evenfs_inode of the "events" directory */