bpf: Propagate error from htab_lock_bucket() to userspace

In __htab_map_lookup_and_delete_batch() if htab_lock_bucket() returns
-EBUSY, it will go to next bucket. Going to next bucket may not only
skip the elements in current bucket silently, but also incur
out-of-bound memory access or expose kernel memory to userspace if
current bucket_cnt is greater than bucket_size or zero.

Fixing it by stopping batch operation and returning -EBUSY when
htab_lock_bucket() fails, and the application can retry or skip the busy
batch as needed.

Fixes: 20b6cc34ea74 ("bpf: Avoid hashtab deadlock with map_locked")
Reported-by: Hao Sun <sunhao.th@gmail.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20220831042629.130006-3-houtao@huaweicloud.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 6fb3b7f..eb1263f 100644 (file)
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1704,8 +1704,11 @@ again_nocopy:
        /* do not grab the lock unless need it (bucket_cnt > 0). */
        if (locked) {
                ret = htab_lock_bucket(htab, b, batch, &flags);
-               if (ret)
-                       goto next_batch;
+               if (ret) {
+                       rcu_read_unlock();
+                       bpf_enable_instrumentation();
+                       goto after_loop;
+               }
        }
 
        bucket_cnt = 0;