diff options
author | Marco Elver <elver@google.com> | 2021-02-09 12:27:01 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-03-04 09:39:35 +0100 |
commit | b343380c0cecd338e87dca306814587798b6c386 (patch) | |
tree | 18c7970d177b1d944b3808c63491b80d24db66ce /kernel/bpf | |
parent | 0fe538319de3bd328c7e721316628a63474bdc3b (diff) |
bpf_lru_list: Read double-checked variable once without lock
[ 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>
Diffstat (limited to 'kernel/bpf')
-rw-r--r-- | kernel/bpf/bpf_lru_list.c | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/kernel/bpf/bpf_lru_list.c b/kernel/bpf/bpf_lru_list.c index e6ef4401a138..9b5eeff72fd3 100644 --- a/kernel/bpf/bpf_lru_list.c +++ b/kernel/bpf/bpf_lru_list.c @@ -505,13 +505,14 @@ struct bpf_lru_node *bpf_lru_pop_free(struct bpf_lru *lru, u32 hash) 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); |