uprobes: Guard against kmemdup() failing in dup_return_instance()

If kmemdup() failed to alloc memory, don't proceed with extra_consumers
copy.

Fixes: e62f2d492728 ("uprobes: Simplify session consumer tracking")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20241206183436.968068-1-andrii@kernel.org

kernel/events/uprobes.c

@@ -2048,6 +2048,8 @@ static struct return_instance *dup_return_instance(struct return_instance *old)
 	struct return_instance *ri;
 
 	ri = kmemdup(old, sizeof(*ri), GFP_KERNEL);
+	if (!ri)
+		return NULL;
 
 	if (unlikely(old->cons_cnt > 1)) {
 		ri->extra_consumers = kmemdup(old->extra_consumers,