Re: [PATCH kernel] tracepoint: Fix race between tracing and removing tracepoint

[Peter Zijlstra]

On Tue, Feb 02, 2021 at 06:23:26PM +1100, Alexey Kardashevskiy wrote:
> When executing a tracepoint, the tracepoint's func is dereferenced twice -
> in __DO_TRACE() (where the returned pointer is checked) and later on in
> __traceiter_##_name where the returned pointer is dereferenced without
> checking which leads to races against tracepoint_removal_sync() and
> crashes.
> 
> This adds a check before referencing the pointer in tracepoint_ptr_deref.

Agreed, a reload got added and it doesn't check the value again.

> Fixes: d25e37d89dd2f ("tracepoint: Optimize using static_call()")
> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>

>  		it_func_ptr =						\
>  			rcu_dereference_raw((&__tracepoint_##_name)->funcs); \

> +		if (it_func_ptr) {					\
> +			do {						\
> +				it_func = (it_func_ptr)->func;		\
> +				__data = (it_func_ptr)->data;		\
> +				((void(*)(void *, proto))(it_func))(__data, args); \
> +			} while ((++it_func_ptr)->func);		\
> +		}							\
>  		return 0;						\


Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>