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Date:   Wed, 18 Apr 2018 13:47:56 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Song Liu <songliubraving@fb.com>
Cc:     <linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
        Ingo Molnar <mingo@redhat.com>,
        Howard McLauchlan <hmclauchlan@fb.com>,
        Josef Bacik <jbacik@fb.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c
Message-ID: <20180418134756.482c899f@gandalf.local.home>
In-Reply-To: <20180418174014.1592871-1-songliubraving@fb.com>
References: <20180418174014.1592871-1-songliubraving@fb.com>
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You forgot to add Miklos again.

Miklos, have any comments on this patch? Or can you give a
"Reviewed-by"?

-- Steve


On Wed, 18 Apr 2018 10:40:14 -0700
Song Liu <songliubraving@fb.com> wrote:

> As Miklos reported and suggested:
> 
>   This pattern repeats two times in trace_uprobe.c and in
>   kernel/events/core.c as well:
> 
>       ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>       if (ret)
>           goto fail_address_parse;
> 
>       inode = igrab(d_inode(path.dentry));
>       path_put(&path);
> 
>   And it's wrong.  You can only hold a reference to the inode if you
>   have an active ref to the superblock as well (which is normally
>   through path.mnt) or holding s_umount.
> 
>   This way unmounting the containing filesystem while the tracepoint is
>   active will give you the "VFS: Busy inodes after unmount..." message
>   and a crash when the inode is finally put.
> 
>   Solution: store path instead of inode.
> 
> This patch fixes two instances in trace_uprobe.c.
> 
> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Howard McLauchlan <hmclauchlan@fb.com>
> Cc: Josef Bacik <jbacik@fb.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------
>  1 file changed, 16 insertions(+), 33 deletions(-)
> 
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 34fd0e0..d9ee522c 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -55,7 +55,7 @@ struct trace_uprobe {
>  	struct list_head		list;
>  	struct trace_uprobe_filter	filter;
>  	struct uprobe_consumer		consumer;
> -	struct inode			*inode;
> +	struct path			path;
>  	char				*filename;
>  	unsigned long			offset;
>  	unsigned long			nhit;
> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>  	for (i = 0; i < tu->tp.nr_args; i++)
>  		traceprobe_free_probe_arg(&tu->tp.args[i]);
>  
> -	iput(tu->inode);
> +	path_put(&tu->path);
>  	kfree(tu->tp.call.class->system);
>  	kfree(tu->tp.call.name);
>  	kfree(tu->filename);
> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>  static int create_trace_uprobe(int argc, char **argv)
>  {
>  	struct trace_uprobe *tu;
> -	struct inode *inode;
>  	char *arg, *event, *group, *filename;
>  	char buf[MAX_EVENT_NAME_LEN];
>  	struct path path;
> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>  	bool is_delete, is_return;
>  	int i, ret;
>  
> -	inode = NULL;
>  	ret = 0;
>  	is_delete = false;
>  	is_return = false;
> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv)
>  	}
>  	/* Find the last occurrence, in case the path contains ':' too. */
>  	arg = strrchr(argv[1], ':');
> -	if (!arg) {
> -		ret = -EINVAL;
> -		goto fail_address_parse;
> -	}
> +	if (!arg)
> +		return -EINVAL;
>  
>  	*arg++ = '\0';
>  	filename = argv[1];
>  	ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>  	if (ret)
> -		goto fail_address_parse;
> -
> -	inode = igrab(d_real_inode(path.dentry));
> -	path_put(&path);
> -
> -	if (!inode || !S_ISREG(inode->i_mode)) {
> -		ret = -EINVAL;
> -		goto fail_address_parse;
> -	}
> +		return ret;
>  
>  	ret = kstrtoul(arg, 0, &offset);
>  	if (ret)
> @@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv)
>  		goto fail_address_parse;
>  	}
>  	tu->offset = offset;
> -	tu->inode = inode;
> +	tu->path = path;
>  	tu->filename = kstrdup(filename, GFP_KERNEL);
>  
>  	if (!tu->filename) {
> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv)
>  	return ret;
>  
>  fail_address_parse:
> -	iput(inode);
> +	path_put(&path);
>  
>  	pr_info("Failed to parse address or file.\n");
>  
> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>  		goto err_flags;
>  
>  	tu->consumer.filter = filter;
> -	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> +	ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
> +			      &tu->consumer);
>  	if (ret)
>  		goto err_buffer;
>  
> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>  
>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>  
> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> +	uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>  	tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>  
>  	uprobe_buffer_disable();
> @@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>  	write_unlock(&tu->filter.rwlock);
>  
>  	if (!done)
> -		return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
> +		return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
> +				    &tu->consumer, false);
>  
>  	return 0;
>  }
> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>  
>  	err = 0;
>  	if (!done) {
> -		err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
> +		err = uprobe_apply(d_inode(tu->path.dentry),
> +				   tu->offset, &tu->consumer, true);
>  		if (err)
>  			uprobe_perf_close(tu, event);
>  	}
> @@ -1337,7 +1328,6 @@ struct trace_event_call *
>  create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  {
>  	struct trace_uprobe *tu;
> -	struct inode *inode;
>  	struct path path;
>  	int ret;
>  
> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  	if (ret)
>  		return ERR_PTR(ret);
>  
> -	inode = igrab(d_inode(path.dentry));
> -	path_put(&path);
> -
> -	if (!inode || !S_ISREG(inode->i_mode)) {
> -		iput(inode);
> -		return ERR_PTR(-EINVAL);
> -	}
> -
>  	/*
>  	 * local trace_kprobes are not added to probe_list, so they are never
>  	 * searched in find_trace_kprobe(). Therefore, there is no concern of
> @@ -1364,11 +1346,12 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  	if (IS_ERR(tu)) {
>  		pr_info("Failed to allocate trace_uprobe.(%d)\n",
>  			(int)PTR_ERR(tu));
> +		path_put(&path);
>  		return ERR_CAST(tu);
>  	}
>  
>  	tu->offset = offs;
> -	tu->inode = inode;
> +	tu->path = path;
>  	tu->filename = kstrdup(name, GFP_KERNEL);
>  	init_trace_event_call(tu, &tu->tp.call);
>