[PATCH 2/5] hwspinlock: Fix race between radix tree insertion and lookup

From: Matthew Wilcox
Date: Wed Jan 27 2016 - 16:19:29 EST


From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>

of_hwspin_lock_get_id() is protected by the RCU lock, which means that
insertions can occur simultaneously with the lookup. If the radix tree
transitions from a height of 0, we can see a slot with the indirect_ptr
bit set, which will cause us to at least read random memory, and could
cause other havoc.

Fix this by using the newly introduced radix_tree_iter_retry().

Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/hwspinlock/hwspinlock_core.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/hwspinlock/hwspinlock_core.c b/drivers/hwspinlock/hwspinlock_core.c
index 52f708bcf77f..d50c701b19d6 100644
--- a/drivers/hwspinlock/hwspinlock_core.c
+++ b/drivers/hwspinlock/hwspinlock_core.c
@@ -313,6 +313,10 @@ int of_hwspin_lock_get_id(struct device_node *np, int index)
hwlock = radix_tree_deref_slot(slot);
if (unlikely(!hwlock))
continue;
+ if (radix_tree_is_indirect_ptr(hwlock)) {
+ slot = radix_tree_iter_retry(&iter);
+ continue;
+ }

if (hwlock->bank->dev->of_node == args.np) {
ret = 0;
--
2.7.0.rc3