Re: [PATCH] s390/syscalls: Fix out of bounds arguments access

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ping

On Thu, Jun 29, 2017 at 11:38:11AM +0200, Jiri Olsa wrote:
> Zorro reported following crash while having enabled
> syscall tracing (CONFIG_FTRACE_SYSCALLS):
> 
>   Unable to handle kernel pointer dereference at virtual ...
>   Oops: 0011 [#1] SMP DEBUG_PAGEALLOC
> 
>   SNIP
> 
>   Call Trace:
>   ([<000000000024d79c>] ftrace_syscall_enter+0xec/0x1d8)
>    [<00000000001099c6>] do_syscall_trace_enter+0x236/0x2f8
>    [<0000000000730f1c>] sysc_tracesys+0x1a/0x32
>    [<000003fffcf946a2>] 0x3fffcf946a2
>   INFO: lockdep is turned off.
>   Last Breaking-Event-Address:
>    [<000000000022dd44>] rb_event_data+0x34/0x40
>   ---[ end trace 8c795f86b1b3f7b9 ]---
> 
> The crash happens in syscall_get_arguments function for
> syscalls with zero arguments, that will try to access
> first argument (args[0]) in event entry, but it's not
> allocated.
> 
> Bail out of there are no arguments.
> 
> Reported-by: Zorro Lang <zlang@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  arch/s390/include/asm/syscall.h | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
> index 6ba0bf928909..5f7c11c932fa 100644
> --- a/arch/s390/include/asm/syscall.h
> +++ b/arch/s390/include/asm/syscall.h
> @@ -64,14 +64,22 @@ static inline void syscall_get_arguments(struct task_struct *task,
>  {
>  	unsigned long mask = -1UL;
>  
> +	/*
> +	 * No arguments for this syscall, there's nothing to do.
> +	 */
> +	if (!n)
> +		return;
> +
>  	BUG_ON(i + n > 6);
>  #ifdef CONFIG_COMPAT
>  	if (test_tsk_thread_flag(task, TIF_31BIT))
>  		mask = 0xffffffff;
>  #endif
> -	while (n-- > 0)
> +	while (n-- > 0) {
>  		if (i + n > 0)
>  			args[n] = regs->gprs[2 + i + n] & mask;
> +	}
> +
>  	if (i == 0)
>  		args[0] = regs->orig_gpr2 & mask;
>  }
> -- 
> 2.9.4
> 
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