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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Thu, 19 Apr 2018 16:44:08 +0200
Message-ID: <CAELBmZBvt=9p8muDsRucR_06kmia9vKT6CMfZbHjQL97N4aFag@mail.gmail.com>
Subject: Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c
To:     Song Liu <songliubraving@fb.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        kernel-team <kernel-team@fb.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Howard McLauchlan <hmclauchlan@fb.com>,
        Josef Bacik <jbacik@fb.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>
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On Thu, Apr 19, 2018 at 10:58 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Wed, Apr 18, 2018 at 7:40 PM, 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));

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


>> -       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