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Date: Thu, 19 Apr 2018 16:37:08 +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 v2] tracing: fix bad use of igrab in trace_uprobe.c
> On Apr 19, 2018, at 7:44 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Thu, Apr 19, 2018 at 10:58 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
>> On Wed, Apr 18, 2018 at 7:40 PM, 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 | 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));
>
> Also, where has the d_real_inode() gone?
>
> Looks like we need tu->inode back, since the return value of
> d_real_inode() may change over time. I'd do the "tu->inode =
> d_real_inode(tu->path.dentry)" just before first use (i.e. when
> enabling the tracepoint).
>
> Thanks,
> Miklos
>
Do we need mechanism to prevent the return value of d_real_inode()
to change? Would the following sequence happen?
create trace_uprobe
enable trace_uprobe (uprobe_register)
d_real changes
disable trace_uprobe (uprobe_unregister get wrong inode?)
Another case might be:
create trace_uprobe
enable trace_uprobe (uprobe_register)
disable trace_uprobe (uprobe_unregister)
d_real changes
enable trace_uprobe (do we need new inode for uprobe_register)
Thanks,
Song
>
>>> - path_put(&path);
>>> -
>>> - if (!inode || !S_ISREG(inode->i_mode)) {
>>
>> Where has the S_ISREG check gone?
>>
>>> - 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)) {
>>
>> And here, again.
>>
>> Otherwise ACK.
>>
>> Also please create a separate patch that removes igrab/iput calls from
>> kernel/events/uprobes.c and adds a comment to the effect that the
>> caller is required to keep the inode (and the containing mount)
>> referenced.
>>
>> Thanks,
>> Miklos
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