Re: [PATCH] x86: profiling: Set prof_cpu_mask to NULL after free

[Chen Zhongjin]

get_maintainer.pl gets a wrong spelled mail address 
'akpm@xxxxxxxxxxxxxxxxxxx'.

Seems it's because Andrew left a wrong Reviewed-by in the last commit.. 
so -cc alone for Andrew.

Sorry for bothering.


On 2023/2/24 16:49, Chen Zhongjin wrote:
> KASAN reported a UAF problem in profile_tick():
>
>    BUG: KASAN: use-after-free in profile_tick+0x5c/0x80
>    Read of size 8 at addr ffff888100928aa0 by task bash/1108
>
>    CPU: 2 PID: 1108 Comm: bash Not tainted 5.10.0+ #72
>    Call Trace:
>     <IRQ>
>     dump_stack+0x93/0xc5
>     print_address_description.constprop.0+0x1c/0x3c0
>     kasan_report.cold+0x37/0x74
>     check_memory_region+0x161/0x1c0
>     profile_tick+0x5c/0x80
>     tick_sched_timer+0xcd/0x100
>     __hrtimer_run_queues+0x23e/0x480
>     hrtimer_interrupt+0x1c2/0x440
>     asm_call_irq_on_stack+0xf/0x20
>     </IRQ>
>    ...
>
> It is beacause in profiling_store(), profile_init() is possible to fail
> and free prof_cpu_mask. However prof_cpu_mask is not set to NULL and
> cpumask_available(prof_cpu_mask) will return true in profile_tick().
> Then cpumask_test_cpu() will dereference prof_cpu_mask and trigger the
> KASAN warning.
>
> There is no interface to disable profile_tick() even though profile_init()
> has been already failed. So just set prof_cpu_mask to NULL when free it.
> Then accessing to prof_cpu_mask can be rejected by prof_buffer or
> cpumask_available().
>
> Fixes: c309b917cab5 ("cpumask: convert kernel/profile.c")
> Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
> ---
>   kernel/profile.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/profile.c b/kernel/profile.c
> index 8a77769bc4b4..d60f9634fb2a 100644
> --- a/kernel/profile.c
> +++ b/kernel/profile.c
> @@ -133,6 +133,7 @@ int __ref profile_init(void)
>   		return 0;
>   
>   	free_cpumask_var(prof_cpu_mask);
> +	prof_cpu_mask = NULL;
>   	return -ENOMEM;
>   }
>   
> @@ -334,7 +335,7 @@ void profile_tick(int type)
>   {
>   	struct pt_regs *regs = get_irq_regs();
>   
> -	if (!user_mode(regs) && cpumask_available(prof_cpu_mask) &&
> +	if (!user_mode(regs) && prof_buffer && cpumask_available(prof_cpu_mask) &&
>   	    cpumask_test_cpu(smp_processor_id(), prof_cpu_mask))
>   		profile_hit(type, (void *)profile_pc(regs));
>   }