[PATCH 5/7] Uprobes/sdt: Prevent multiple reference counter for same uprobe

[Ravi Bangoria <ravi.bangoria@linux.ibm.com>]

Even if we don't allow to create same uprobe with different reference
counter offset via trace_uprobe, user can still create such uprobes
by creating one uprobe using trace_uprobe and other by directly
calling uprobe_register() from kernel module. Prevent such scenarios.

Note that, we are restricting user to not use both ways (trace_uprobe
and kernel module) simultaneously. Ex, User can not trace single uprobe
(with reference counter) simultaneously with Systemtap and perf at the
same time.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
---
 kernel/events/uprobes.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 279c8fc..5e07f99 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -526,6 +526,12 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
 	cur_uprobe = insert_uprobe(uprobe);
 	/* a uprobe exists for this inode:offset combination */
 	if (cur_uprobe) {
+		if (cur_uprobe->ref_ctr_offset != uprobe->ref_ctr_offset) {
+			pr_warn("Err: Reference counter mismatch.\n");
+			put_uprobe(cur_uprobe);
+			kfree(uprobe);
+			return ERR_PTR(-EINVAL);
+		}
 		kfree(uprobe);
 		uprobe = cur_uprobe;
 	}
@@ -1184,6 +1190,9 @@ static int __uprobe_register(struct inode *inode, loff_t offset,
 	uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
 	if (!uprobe)
 		return -ENOMEM;
+	if (IS_ERR(uprobe))
+		return PTR_ERR(uprobe);
+
 	/*
 	 * We can race with uprobe_unregister()->delete_uprobe().
 	 * Check uprobe_is_active() and retry if it is false.
-- 
1.8.3.1

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