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Subject[PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c
Date
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 | 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));
- 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;
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);
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->filename = kstrdup(name, GFP_KERNEL);
init_trace_event_call(tu, &tu->tp.call);

--
2.9.5
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