[PATCH v9 2/4] Uprobes/sdt: Prevent multiple reference counter for same uprobe

[Ravi Bangoria]

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

Signed-off-by: Ravi Bangoria <ravi.bango...@linux.ibm.com>
Acked-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
Reviewed-by: Oleg Nesterov <o...@redhat.com>
---
 kernel/events/uprobes.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 35065febcb6c..ecee371a59c7 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -679,6 +679,16 @@ static struct uprobe *insert_uprobe(struct uprobe *uprobe)
        return u;
 }
 
+static void
+ref_ctr_mismatch_warn(struct uprobe *cur_uprobe, struct uprobe *uprobe)
+{
+       pr_warn("ref_ctr_offset mismatch. inode: 0x%lx offset: 0x%llx "
+               "ref_ctr_offset(old): 0x%llx ref_ctr_offset(new): 0x%llx\n",
+               uprobe->inode->i_ino, (unsigned long long) uprobe->offset,
+               (unsigned long long) cur_uprobe->ref_ctr_offset,
+               (unsigned long long) uprobe->ref_ctr_offset);
+}
+
 static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
                                   loff_t ref_ctr_offset)
 {
@@ -698,6 +708,12 @@ 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) {
+                       ref_ctr_mismatch_warn(cur_uprobe, uprobe);
+                       put_uprobe(cur_uprobe);
+                       kfree(uprobe);
+                       return ERR_PTR(-EINVAL);
+               }
                kfree(uprobe);
                uprobe = cur_uprobe;
        }
@@ -1112,6 +1128,9 @@ 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.
-- 
2.14.4