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Date: Wed, 18 Apr 2018 16:08:50 +0000
From: Song Liu <songliubraving@...com>
To: Miklos Szeredi <miklos@...redi.hu>
CC: LKML <linux-kernel@...r.kernel.org>,
Kernel Team <Kernel-team@...com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
"Howard McLauchlan" <hmclauchlan@...com>,
Josef Bacik <jbacik@...com>,
"Srikar Dronamraju" <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c
> On Apr 18, 2018, at 7:03 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Wed, Apr 18, 2018 at 8:29 AM, Song Liu <songliubraving@...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@...dmis.org>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Howard McLauchlan <hmclauchlan@...com>
>> Cc: Josef Bacik <jbacik@...com>
>> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
>> Reported-by: Miklos Szeredi <miklos@...redi.hu>
>> Signed-off-by: Song Liu <songliubraving@...com>
>> ---
>> kernel/trace/trace_uprobe.c | 42 ++++++++++++++----------------------------
>> 1 file changed, 14 insertions(+), 28 deletions(-)
>>
>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>> index 0d450b4..80dfcdf 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;
>> @@ -448,14 +446,6 @@ static int create_trace_uprobe(int argc, char **argv)
>> if (ret)
>> goto fail_address_parse;
>>
>> - inode = igrab(d_inode(path.dentry));
>
> This is not against -linus tree.
These patches are against tip/perf/core. I can also send version against
-linus tree.
>
>> - path_put(&path);
>> -
>> - if (!inode || !S_ISREG(inode->i_mode)) {
>> - ret = -EINVAL;
>> - goto fail_address_parse;
>> - }
>> -
>> ret = kstrtoul(arg, 0, &offset);
>> if (ret)
>> goto fail_address_parse;
>> @@ -490,7 +480,8 @@ static int create_trace_uprobe(int argc, char **argv)
>> goto fail_address_parse;
>> }
>> tu->offset = offset;
>> - tu->inode = inode;
>> + tu->path.mnt = path.mnt;
>> + tu->path.dentry = path.dentry;
>
> You can just assign the whole structure. No need to mess with
> individual members.
>
> tu->path = path;
Will fix in v2.
>
>> tu->filename = kstrdup(filename, GFP_KERNEL);
>>
>> if (!tu->filename) {
>> @@ -558,7 +549,7 @@ 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");
>>
>> @@ -937,7 +928,8 @@ 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);
>
> It is not entirely clear how the lifetime of uprobe relates to the
> lifetime of trace_uprobe. Is the uprobe object never going to survive
> its creator trace_uprobe object?
>
> If that's the case, it warrants a comment. If that's not the case,
> then the path would need to be passed to uprobe_resister() which would
> need to obtain its own reference.
trace_uprobe will not be freed before the uprobe object. trace_uprobe
holds reference to struct path (with path_get()).
>
>> if (ret)
>> goto err_buffer;
>>
>> @@ -981,7 +973,7 @@ 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();
>> @@ -1056,7 +1048,8 @@ 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;
>> }
>> @@ -1088,7 +1081,8 @@ 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);
>> }
>> @@ -1352,7 +1346,6 @@ 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;
>>
>> @@ -1360,14 +1353,6 @@ 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
>> @@ -1383,7 +1368,8 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>> }
>>
>> tu->offset = offs;
>> - tu->inode = inode;
>> + tu->path.mnt = path.mnt;
>> + tu->path.dentry = path.dentry;
>
> tu->path = path
>
>
>> tu->filename = kstrdup(name, GFP_KERNEL);
>> init_trace_event_call(tu, &tu->tp.call);
>>
>> --
>> 2.9.5
>>
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