[PATCH v3 1/2] lib/idr: fix infinite loop in idr_get_next()

[Josh Law]

In idr_get_next(), if the returned id from idr_get_next_ul() is greater
than INT_MAX, the function issues a warning and returns NULL without
updating the *nextid pointer. This causes a soft lockup for any caller
iterating over an IDR (e.g. via idr_for_each_entry) because they will
receive NULL, fail to advance their index, and repeatedly query the same
state forever.

Fix this by setting *nextid to INT_MAX when the bounds check fails,
ensuring the caller's iteration will terminate.

Also update the idr_get_next() test case in the radix-tree test suite
to expect INT_MAX instead of 0 when hitting this condition.

Signed-off-by: Josh Law <objecting@xxxxxxxxxxxxx>
---
 lib/idr.c                           | 4 +++-
 tools/testing/radix-tree/idr-test.c | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/idr.c b/lib/idr.c
index f25bd2b9e9a4..07098eb4ddc3 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -268,8 +268,10 @@ void *idr_get_next(struct idr *idr, int *nextid)
 	unsigned long id = *nextid;
 	void *entry = idr_get_next_ul(idr, &id);
 
-	if (WARN_ON_ONCE(id > INT_MAX))
+	if (WARN_ON_ONCE(id > INT_MAX)) {
+		*nextid = INT_MAX;
 		return NULL;
+	}
 	*nextid = id;
 	return entry;
 }
diff --git a/tools/testing/radix-tree/idr-test.c b/tools/testing/radix-tree/idr-test.c
index 945144e98507..bf6a0da6a50a 100644
--- a/tools/testing/radix-tree/idr-test.c
+++ b/tools/testing/radix-tree/idr-test.c
@@ -213,7 +213,7 @@ void idr_u32_test1(struct idr *idr, u32 handle)
 	ptr = idr_get_next(idr, &sid);
 	if (id > INT_MAX) {
 		BUG_ON(ptr != NULL);
-		BUG_ON(sid != 0);
+		BUG_ON(sid != INT_MAX);
 	} else {
 		BUG_ON(ptr != DUMMY_PTR);
 		BUG_ON(sid != id);
-- 
2.34.1