bpf: Ensure correct locking around vulnerable function find_vpid()

The documentation for find_vpid() clearly states:

  "Must be called with the tasklist_lock or rcu_read_lock() held."

Presently we do neither for find_vpid() instance in bpf_task_fd_query().
Add proper rcu_read_lock/unlock() to fix the issue.

Fixes: 41bdc4b40ed6f ("bpf: introduce bpf subcommand BPF_TASK_FD_QUERY")
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220912133855.1218900-1-lee@kernel.org

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 2776062..1bd18af 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4395,7 +4395,9 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
        if (attr->task_fd_query.flags != 0)
                return -EINVAL;
 
+       rcu_read_lock();
        task = get_pid_task(find_vpid(pid), PIDTYPE_PID);
+       rcu_read_unlock();
        if (!task)
                return -ENOENT;