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Message-ID: <CAELBmZBvt=9p8muDsRucR_06kmia9vKT6CMfZbHjQL97N4aFag@mail.gmail.com>
Date: Thu, 19 Apr 2018 16:44:08 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Song Liu <songliubraving@...com>
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 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
>> - 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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