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Date: Wed, 18 Apr 2018 16:03:42 +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 1/2] tracing: fix bad use of igrab in trace_uprobe.c
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.
> - 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;
> 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.
> 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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