[ Upstream commit
6df8fb83301d68ea0a0c0e1cbcc790fcc333ed12 ]
For double-checked locking in bpf_common_lru_push_free(), node->type is
read outside the critical section and then re-checked under the lock.
However, concurrent writes to node->type result in data races.
For example, the following concurrent access was observed by KCSAN:
write to 0xffff88801521bc22 of 1 bytes by task 10038 on cpu 1:
__bpf_lru_node_move_in kernel/bpf/bpf_lru_list.c:91
__local_list_flush kernel/bpf/bpf_lru_list.c:298
...
read to 0xffff88801521bc22 of 1 bytes by task 10043 on cpu 0:
bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:507
bpf_lru_push_free kernel/bpf/bpf_lru_list.c:555
...
Fix the data races where node->type is read outside the critical section
(for double-checked locking) by marking the access with READ_ONCE() as
well as ensuring the variable is only accessed once.
Fixes:
3a08c2fd7634 ("bpf: LRU List")
Reported-by: syzbot+3536db46dfa58c573458@syzkaller.appspotmail.com
Reported-by: syzbot+516acdb03d3e27d91bcd@syzkaller.appspotmail.com
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210209112701.3341724-1-elver@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
static void bpf_common_lru_push_free(struct bpf_lru *lru,
struct bpf_lru_node *node)
{
+ u8 node_type = READ_ONCE(node->type);
unsigned long flags;
- if (WARN_ON_ONCE(node->type == BPF_LRU_LIST_T_FREE) ||
- WARN_ON_ONCE(node->type == BPF_LRU_LOCAL_LIST_T_FREE))
+ if (WARN_ON_ONCE(node_type == BPF_LRU_LIST_T_FREE) ||
+ WARN_ON_ONCE(node_type == BPF_LRU_LOCAL_LIST_T_FREE))
return;
- if (node->type == BPF_LRU_LOCAL_LIST_T_PENDING) {
+ if (node_type == BPF_LRU_LOCAL_LIST_T_PENDING) {
struct bpf_lru_locallist *loc_l;
loc_l = per_cpu_ptr(lru->common_lru.local_list, node->cpu);