Subject: [PATCH] arm64: check for number of arguments in syscall_get/set_arguments()

From: [email-masked] (AKASHI Takahiro)
Date: Wed, 02 Oct 2013 15:45:49 +0900

On 10/01/2013 06:19 PM, Will Deacon wrote:
> On Tue, Oct 01, 2013 at 06:33:04AM +0100, AKASHI Takahiro wrote:
>> In ftrace_syscall_enter(),
>>      syscall_get_arguments(..., 0, n, ...)
>> 	if (i == 0) { <handle orig_x0> ...; n--;}
>> 	memcpy(..., n * sizeof(args[0]));
>> If 'number of arguments(n)' is zero and 'argument index(i)' is also zero in
>> syscall_get_arguments(), none of arguments should be copied by memcpy().
>> Otherwise 'n--' can be a big positive number and unexpected amount of data
>> will be copied. Tracing system calls which take no argument, say sync(void),
>> may hit this case and eventually make the system corrupted.
>> This patch fixes the issue both in syscall_get_arguments() and
>> syscall_set_arguments().
>>
>> Please note, however, that asm-generic/syscall.h says,
>>   * syscall_get_arguments - extract system call parameter values
>>   * @i:          argument index [0,5]
>>   * @n:          number of arguments; n+i must be [1,6].
>> and so we'd better change the caller's code(ftrace_syscall_enter).
>
> Since (most) other architectures deal with n+i == 0, please can you submit a
> separate patch updating that comment?

Yes, I will. But is the patch that only modifies a comment acceptable?

>> Signed-off-by: AKASHI Takahiro <[email-masked]>
>> ---
>>   arch/arm64/include/asm/syscall.h |    6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
>> index c89821f..01bb8cc 100644
>> --- a/arch/arm64/include/asm/syscall.h
>> +++ b/arch/arm64/include/asm/syscall.h
>> @@ -63,6 +63,9 @@ static inline void syscall_get_arguments(struct task_struct *task,
>>   					 unsigned int i, unsigned int n,
>>   					 unsigned long *args)
>>   {
>> +	if (n == 0)
>> +		return;
>> +
>>   	if (i + n > SYSCALL_MAX_ARGS) {
>>   		unsigned long *args_bad = args + SYSCALL_MAX_ARGS - i;
>>   		unsigned int n_bad = n + i - SYSCALL_MAX_ARGS;
>> @@ -86,6 +89,9 @@ static inline void syscall_set_arguments(struct task_struct *task,
>>   					 unsigned int i, unsigned int n,
>>   					 const unsigned long *args)
>>   {
>> +	if (n == 0)
>> +		return;
>> +
>
> Looks sensible. Please can you fix arch/arm/ as well?

Yes, I will.

-Takahiro AKASHI

> Cheers,
> Will