linux-kernel - [for-next][PATCH 4/5] trace_uprobe/sdt: Prevent multiple reference counter for same uprobe

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Message-Id: <20180926161336.698132369@goodmis.org>
Date:   Wed, 26 Sep 2018 12:12:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Song Liu <songliubraving@...com>,
        Oleg Nesterov <oleg@...hat.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: [for-next][PATCH 4/5] trace_uprobe/sdt: Prevent multiple reference counter for same uprobe

From: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>

We assume to have only one reference counter for one uprobe.
Don't allow user to add multiple trace_uprobe entries having
same inode+offset but different reference counter.

Ex,
  # echo "p:sdt_tick/loop2 /home/ravi/tick:0x6e4(0x10036)" > uprobe_events
  # echo "p:sdt_tick/loop2_1 /home/ravi/tick:0x6e4(0xfffff)" >> uprobe_events
  bash: echo: write error: Invalid argument

  # dmesg
  trace_kprobe: Reference counter offset mismatch.

There is one exception though:
When user is trying to replace the old entry with the new
one, we allow this if the new entry does not conflict with
any other existing entries.

Link: http://lkml.kernel.org/r/20180820044250.11659-4-ravi.bangoria@linux.ibm.com

Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Reviewed-by: Song Liu <songliubraving@...com>
Reviewed-by: Oleg Nesterov <oleg@...hat.com>
Tested-by: Song Liu <songliubraving@...com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace_uprobe.c | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 7b85172beab6..3a7c73c40007 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -312,6 +312,35 @@ static int unregister_trace_uprobe(struct trace_uprobe *tu)
 	return 0;
 }
 
+/*
+ * Uprobe with multiple reference counter is not allowed. i.e.
+ * If inode and offset matches, reference counter offset *must*
+ * match as well. Though, there is one exception: If user is
+ * replacing old trace_uprobe with new one(same group/event),
+ * then we allow same uprobe with new reference counter as far
+ * as the new one does not conflict with any other existing
+ * ones.
+ */
+static struct trace_uprobe *find_old_trace_uprobe(struct trace_uprobe *new)
+{
+	struct trace_uprobe *tmp, *old = NULL;
+	struct inode *new_inode = d_real_inode(new->path.dentry);
+
+	old = find_probe_event(trace_event_name(&new->tp.call),
+				new->tp.call.class->system);
+
+	list_for_each_entry(tmp, &uprobe_list, list) {
+		if ((old ? old != tmp : true) &&
+		    new_inode == d_real_inode(tmp->path.dentry) &&
+		    new->offset == tmp->offset &&
+		    new->ref_ctr_offset != tmp->ref_ctr_offset) {
+			pr_warn("Reference counter offset mismatch.");
+			return ERR_PTR(-EINVAL);
+		}
+	}
+	return old;
+}
+
 /* Register a trace_uprobe and probe_event */
 static int register_trace_uprobe(struct trace_uprobe *tu)
 {
@@ -321,8 +350,12 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
 	mutex_lock(&uprobe_lock);
 
 	/* register as an event */
-	old_tu = find_probe_event(trace_event_name(&tu->tp.call),
-			tu->tp.call.class->system);
+	old_tu = find_old_trace_uprobe(tu);
+	if (IS_ERR(old_tu)) {
+		ret = PTR_ERR(old_tu);
+		goto end;
+	}
+
 	if (old_tu) {
 		/* delete old event */
 		ret = unregister_trace_uprobe(old_tu);
-- 
2.18.0