[PATCH] firewire: core: fix race condition in split transaction handling

[Takashi Sakamoto]

For a split transaction, either fw_core_handle_response() or
split_transaction_timeout_callback() may manipulate the same transaction
entry in the pending transaction list. The return value of timer_delete()
is used to determine which function handles the entry. If the transaction
is a split transaction and timer_delete() returns zero, the timeout
callback may already be running. In this case, the response handler must
leave the entry in the list for the timeout callback to remove.

A previous code refactoring broke this behavior, introducing a race
condition in which both functions could process the same transaction.
This could lead to a use-after-free on the transaction initiator side.

Fix the regression by ensuring that the response handler does not process
the transaction when timer_delete() returns zero. The timeout callback is
responsible for removing the entry from the pending transaction list.

Fixes: fa2dc2710076 ("firewire: core: code refactoring to find and pop transaction entry")
Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
---
 drivers/firewire/core-transaction.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index 22ae387ae03c..016070560c74 100644
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -89,8 +89,12 @@ void fw_cancel_pending_transactions(struct fw_card *card)
 			break;						\
 		}							\
 	}								\
-	if (t && try_cancel_split_timeout(t))				\
-		remove_transaction_entry(card, t);			\
+	if (t) {							\
+		if (try_cancel_split_timeout(t))			\
+			remove_transaction_entry(card, t);		\
+		else							\
+			t = NULL;					\
+	}								\
 	t;								\
 })
 
-- 
2.53.0