Re: [PATCH 1/2] bpf: Invoke __bpf_prog_exit_sleepable_recur() on recursion in kern_sys_bpf().

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Aug 30, 2023 at 10:04:04AM +0200, Sebastian Andrzej Siewior wrote:
> If __bpf_prog_enter_sleepable_recur() detects recursion then it returns
> 0 without undoing rcu_read_lock_trace(), migrate_disable() or
> decrementing the recursion counter. This is fine in the JIT case because
> the JIT code will jump in the 0 case to the end and invoke the matching
> exit trampoline (__bpf_prog_exit_sleepable_recur()).
> 
> This is not the case in kern_sys_bpf() which returns directly to the
> caller with an error code.
> 
> Add __bpf_prog_exit_sleepable_recur() as clean up in the recursion case.
> 
> Fixes: b1d18a7574d0d ("bpf: Extend sys_bpf commands for bpf_syscall programs.")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  kernel/bpf/syscall.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index a2aef900519c2..c925c270ed8b4 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -5307,6 +5307,7 @@ int kern_sys_bpf(int cmd, union bpf_attr *attr, unsigned int size)
>  		run_ctx.saved_run_ctx = NULL;
>  		if (!__bpf_prog_enter_sleepable_recur(prog, &run_ctx)) {
>  			/* recursion detected */
> +			__bpf_prog_exit_sleepable_recur(prog, 0, &run_ctx);
>  			bpf_prog_put(prog);
>  			return -EBUSY;
>  		}
> -- 
> 2.40.1
>