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Message-Id: <20230908164553.aff280695dd77b2b9cab35b8@kernel.org>
Date: Fri, 8 Sep 2023 16:45:53 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Masami Hiramatsu <mhiramat@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Zheng Yejian <zhengyejian1@...wei.com>,
Naresh Kamboju <naresh.kamboju@...aro.org>,
Ajay Kaher <akaher@...are.com>
Subject: Re: [PATCH 1/6] tracefs/eventfs: Use dput to free the toplevel
events directory
Hi,
On Wed, 06 Sep 2023 22:47:11 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
>
> Currently when rmdir on an instance is done, eventfs_remove_events_dir()
> is called and it does a dput on the dentry and then frees the
> eventfs_inode that represents the events directory.
>
> But there's no protection against a reader reading the top level events
> directory at the same time and we can get a use after free error. Instead,
> use the dput() associated to the dentry to also free the eventfs_inode
> associated to the events directory, as that will get called when the last
> reference to the directory is released.
>
> Link: https://lore.kernel.org/all/1cb3aee2-19af-c472-e265-05176fe9bd84@huawei.com/
>
> Cc: Ajay Kaher <akaher@...are.com>
> Fixes: 5bdcd5f5331a2 eventfs: ("Implement removal of meta data from eventfs")
> Reported-by: Zheng Yejian <zhengyejian1@...wei.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
> Changes since v1: https://lore.kernel.org/linux-trace-kernel/20230905183332.628d7cc0@gandalf.local.home
> - Removed left over "ei" variable (kernel test robot)
>
> fs/tracefs/event_inode.c | 17 ++++++++++++-----
> fs/tracefs/inode.c | 2 +-
> fs/tracefs/internal.h | 5 +++--
> 3 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
> index fa1a1679a886..609ccb5b7cfc 100644
> --- a/fs/tracefs/event_inode.c
> +++ b/fs/tracefs/event_inode.c
> @@ -185,17 +185,27 @@ static struct dentry *create_dir(const char *name, struct dentry *parent, void *
>
> /**
> * eventfs_set_ef_status_free - set the ef->status to free
> + * @ti: the tracefs_inode of the dentry
> * @dentry: dentry who's status to be freed
> *
> * eventfs_set_ef_status_free will be called if no more
> * references remain
> */
> -void eventfs_set_ef_status_free(struct dentry *dentry)
> +void eventfs_set_ef_status_free(struct tracefs_inode *ti, struct dentry *dentry)
> {
> struct tracefs_inode *ti_parent;
> + struct eventfs_inode *ei;
> struct eventfs_file *ef;
>
> mutex_lock(&eventfs_mutex);
> +
> + /* The top level events directory may be freed by this */
> + if (unlikely(ti->flags & TRACEFS_EVENT_TOP_INODE)) {
> + ei = ti->private;
> + kfree(ei);
Don't we need to clear 'ti->private' here to avoid accessing
(or double free) ti->private somewhare?
> + goto out;
> + }
> +
> ti_parent = get_tracefs(dentry->d_parent->d_inode);
> if (!ti_parent || !(ti_parent->flags & TRACEFS_EVENT_INODE))
> goto out;
Here, I guess this "!(ti_parent->flags & TRACEFS_EVENT_INODE)" means this
inode is TRACEFS_EVENT_TOP_INODE, so this check may not be needed,
is this correct?
Thank you,
> @@ -510,7 +520,7 @@ struct dentry *eventfs_create_events_dir(const char *name,
> INIT_LIST_HEAD(&ei->e_top_files);
>
> ti = get_tracefs(inode);
> - ti->flags |= TRACEFS_EVENT_INODE;
> + ti->flags |= TRACEFS_EVENT_INODE | TRACEFS_EVENT_TOP_INODE;
> ti->private = ei;
>
> inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
> @@ -806,7 +816,6 @@ void eventfs_remove(struct eventfs_file *ef)
> void eventfs_remove_events_dir(struct dentry *dentry)
> {
> struct tracefs_inode *ti;
> - struct eventfs_inode *ei;
>
> if (!dentry || !dentry->d_inode)
> return;
> @@ -815,8 +824,6 @@ void eventfs_remove_events_dir(struct dentry *dentry)
> if (!ti || !(ti->flags & TRACEFS_EVENT_INODE))
> return;
>
> - ei = ti->private;
> d_invalidate(dentry);
> dput(dentry);
> - kfree(ei);
> }
> diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
> index 3b8dd938b1c8..891653ba9cf3 100644
> --- a/fs/tracefs/inode.c
> +++ b/fs/tracefs/inode.c
> @@ -385,7 +385,7 @@ static void tracefs_dentry_iput(struct dentry *dentry, struct inode *inode)
>
> ti = get_tracefs(inode);
> if (ti && ti->flags & TRACEFS_EVENT_INODE)
> - eventfs_set_ef_status_free(dentry);
> + eventfs_set_ef_status_free(ti, dentry);
> iput(inode);
> }
>
> diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
> index 69c2b1d87c46..4f2e49e2197b 100644
> --- a/fs/tracefs/internal.h
> +++ b/fs/tracefs/internal.h
> @@ -3,7 +3,8 @@
> #define _TRACEFS_INTERNAL_H
>
> enum {
> - TRACEFS_EVENT_INODE = BIT(1),
> + TRACEFS_EVENT_INODE = BIT(1),
> + TRACEFS_EVENT_TOP_INODE = BIT(2),
> };
>
> struct tracefs_inode {
> @@ -24,6 +25,6 @@ struct inode *tracefs_get_inode(struct super_block *sb);
> struct dentry *eventfs_start_creating(const char *name, struct dentry *parent);
> struct dentry *eventfs_failed_creating(struct dentry *dentry);
> struct dentry *eventfs_end_creating(struct dentry *dentry);
> -void eventfs_set_ef_status_free(struct dentry *dentry);
> +void eventfs_set_ef_status_free(struct tracefs_inode *ti, struct dentry *dentry);
>
> #endif /* _TRACEFS_INTERNAL_H */
> --
> 2.40.1
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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