[PATCH 3.16 233/366] tracing: Fix bad use of igrab in trace_uprobe.c

Ben Hutchings
2018-10-14T23:11:45Z

From: Song Liu <songliubraving@fb.com>

commit 0c92c7a3c5d416f47b32c5f20a611dfeca5d5f2e upstream.

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. struct path is added to
struct trace_uprobe to keep the inode and containing mount point
referenced.

Link: http://lkml.kernel.org/r/20180423172135.4050588-1-songliubraving@fb.com

Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
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>
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
[bwh: Backported to 3.16:
- Open-code d_real_inode(), d_is_reg()
- Drop changes in create_local_trace_uprobe()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/trace/trace_uprobe.c | 35 ++++++++++++++---------------------
1 file changed, 14 insertions(+), 21 deletions(-)

--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -53,6 +53,7 @@ struct trace_uprobe {
struct list_head list;
struct trace_uprobe_filter filter;
struct uprobe_consumer consumer;
+ struct path path;
struct inode *inode;
char *filename;
unsigned long offset;
@@ -284,7 +285,7 @@ static void free_trace_uprobe(struct tra
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);
@@ -358,7 +359,6 @@ end:
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;
@@ -366,7 +366,6 @@ static int create_trace_uprobe(int argc,
bool is_delete, is_return;
int i, ret;

- inode = NULL;
ret = 0;
is_delete = false;
is_return = false;
@@ -432,21 +431,16 @@ static int create_trace_uprobe(int argc,
}
/* 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(path.dentry->d_inode);
- path_put(&path);
+ return ret;

- if (!inode || !S_ISREG(inode->i_mode)) {
+ if (!S_ISREG(path.dentry->d_inode->i_mode)) {
ret = -EINVAL;
goto fail_address_parse;
}
@@ -485,7 +479,7 @@ static int create_trace_uprobe(int argc,
goto fail_address_parse;
}
tu->offset = offset;
- tu->inode = inode;
+ tu->path = path;
tu->filename = kstrdup(filename, GFP_KERNEL);

if (!tu->filename) {
@@ -552,7 +546,7 @@ error:
return ret;

fail_address_parse:
- iput(inode);
+ path_put(&path);

pr_info("Failed to parse address or file.\n");

@@ -919,6 +913,7 @@ probe_event_enable(struct trace_uprobe *
goto err_flags;

tu->consumer.filter = filter;
+ tu->inode = tu->path.dentry->d_inode;
ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
if (ret)
goto err_buffer;
@@ -964,6 +959,7 @@ probe_event_disable(struct trace_uprobe
WARN_ON(!uprobe_filter_is_empty(&tu->filter));

uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
+ tu->inode = NULL;
tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;

uprobe_buffer_disable();