[PATCH] idr: Prevent unintended underflow for the idr index

[Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>]

It is possible for unaware callers of several idr functions to accidentally
underflow the index by specifying a id that is less than the idr base.

Signed-off-by: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>
---

 lib/idr.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/idr.c b/lib/idr.c
index 66a3748..d9e180c 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -151,6 +151,9 @@ EXPORT_SYMBOL(idr_alloc_cyclic);
  */
 void *idr_remove(struct idr *idr, unsigned long id)
 {
+	if (id < idr->idr_base)
+		return NULL;
+
 	return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
 }
 EXPORT_SYMBOL_GPL(idr_remove);
@@ -171,6 +174,9 @@ EXPORT_SYMBOL_GPL(idr_remove);
  */
 void *idr_find(const struct idr *idr, unsigned long id)
 {
+	if (id < idr->idr_base)
+		return NULL;
+
 	return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
 }
 EXPORT_SYMBOL_GPL(idr_find);
@@ -302,6 +308,9 @@ void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
 	void __rcu **slot = NULL;
 	void *entry;
 
+	if (id < idr->idr_base)
+		return ERR_PTR(-ENOENT);
+
 	id -= idr->idr_base;
 
 	entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
-- 
2.7.4