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From:   Song Liu <songliubraving@fb.com>
To:     Steven Rostedt <rostedt@goodmis.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Kernel Team <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
Thread-Topic: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c
Thread-Index: AQHT1zxd/hOH+TsgmUiWuxUvrApKJqQGzEsAgAAAzwA=
Date:   Wed, 18 Apr 2018 17:50:51 +0000
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References: <20180418174014.1592871-1-songliubraving@fb.com>
 <20180418134756.482c899f@gandalf.local.home>
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> On Apr 18, 2018, at 10:47 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
>=20
> You forgot to add Miklos again.
>=20

I am really sorry! I was expecting "Reported-by" to add Miklos.

Song


> Miklos, have any comments on this patch? Or can you give a
> "Reviewed-by"?
>=20
> -- Steve
>=20
>=20
> On Wed, 18 Apr 2018 10:40:14 -0700
> Song Liu <songliubraving@fb.com> wrote:
>=20
>> As Miklos reported and suggested:
>>=20
>>  This pattern repeats two times in trace_uprobe.c and in
>>  kernel/events/core.c as well:
>>=20
>>      ret =3D kern_path(filename, LOOKUP_FOLLOW, &path);
>>      if (ret)
>>          goto fail_address_parse;
>>=20
>>      inode =3D igrab(d_inode(path.dentry));
>>      path_put(&path);
>>=20
>>  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.
>>=20
>>  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.
>>=20
>>  Solution: store path instead of inode.
>>=20
>> This patch fixes two instances in trace_uprobe.c.
>>=20
>> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobe=
s")
>> 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(-)
>>=20
>> 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 *t=
u)
>> 	for (i =3D 0; i < tu->tp.nr_args; i++)
>> 		traceprobe_free_probe_arg(&tu->tp.args[i]);
>>=20
>> -	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;
>>=20
>> -	inode =3D NULL;
>> 	ret =3D 0;
>> 	is_delete =3D false;
>> 	is_return =3D false;
>> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **ar=
gv)
>> 	}
>> 	/* Find the last occurrence, in case the path contains ':' too. */
>> 	arg =3D strrchr(argv[1], ':');
>> -	if (!arg) {
>> -		ret =3D -EINVAL;
>> -		goto fail_address_parse;
>> -	}
>> +	if (!arg)
>> +		return -EINVAL;
>>=20
>> 	*arg++ =3D '\0';
>> 	filename =3D argv[1];
>> 	ret =3D kern_path(filename, LOOKUP_FOLLOW, &path);
>> 	if (ret)
>> -		goto fail_address_parse;
>> -
>> -	inode =3D igrab(d_real_inode(path.dentry));
>> -	path_put(&path);
>> -
>> -	if (!inode || !S_ISREG(inode->i_mode)) {
>> -		ret =3D -EINVAL;
>> -		goto fail_address_parse;
>> -	}
>> +		return ret;
>>=20
>> 	ret =3D 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 =3D offset;
>> -	tu->inode =3D inode;
>> +	tu->path =3D path;
>> 	tu->filename =3D kstrdup(filename, GFP_KERNEL);
>>=20
>> 	if (!tu->filename) {
>> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv=
)
>> 	return ret;
>>=20
>> fail_address_parse:
>> -	iput(inode);
>> +	path_put(&path);
>>=20
>> 	pr_info("Failed to parse address or file.\n");
>>=20
>> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct t=
race_event_file *file,
>> 		goto err_flags;
>>=20
>> 	tu->consumer.filter =3D filter;
>> -	ret =3D uprobe_register(tu->inode, tu->offset, &tu->consumer);
>> +	ret =3D uprobe_register(d_inode(tu->path.dentry), tu->offset,
>> +			      &tu->consumer);
>> 	if (ret)
>> 		goto err_buffer;
>>=20
>> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct =
trace_event_file *file)
>>=20
>> 	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>>=20
>> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>> +	uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer)=
;
>> 	tu->tp.flags &=3D file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>>=20
>> 	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);
>>=20
>> 	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);
>>=20
>> 	return 0;
>> }
>> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *t=
u, struct perf_event *event)
>>=20
>> 	err =3D 0;
>> 	if (!done) {
>> -		err =3D uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
>> +		err =3D 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;
>>=20
>> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned lo=
ng offs, bool is_return)
>> 	if (ret)
>> 		return ERR_PTR(ret);
>>=20
>> -	inode =3D 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 l=
ong 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);
>> 	}
>>=20
>> 	tu->offset =3D offs;
>> -	tu->inode =3D inode;
>> +	tu->path =3D path;
>> 	tu->filename =3D kstrdup(name, GFP_KERNEL);
>> 	init_trace_event_call(tu, &tu->tp.call);
>>=20
>=20