idr: Handle integer overflow correctly

If there is an entry at INT_MAX then idr_for_each_entry() will increment
id after handling it.  This is undefined behaviour, and is caught by
UBSAN.  Adding 1U to id forces the operation to be carried out as an
unsigned addition which (when assigned to id) will result in INT_MIN.
Since there is never an entry stored at INT_MIN, idr_get_next() will
return NULL, ending the loop as expected.

Signed-off-by: Matthew Wilcox <willy@infradead.org>

diff --git a/include/linux/idr.h b/include/linux/idr.h
index 6e556350857a3daf58a35e046376a37deab6eb80..13bb71eb4fd96312a4bda477c4df43d20628c6de 100644 (file)
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -136,7 +136,7 @@ static inline bool idr_is_empty(const struct idr *idr)
  * is convenient for a "not found" value.
  */
 #define idr_for_each_entry(idr, entry, id)                     \
-       for (id = 0; ((entry) = idr_get_next(idr, &(id))) != NULL; ++id)
+       for (id = 0; ((entry) = idr_get_next(idr, &(id))) != NULL; id += 1U)
 
 /**
  * idr_for_each_entry_continue() - Continue iteration over an IDR's elements of a given type