On Mon, 25 Jan 2016, James Hogan wrote:
> Since commit 4c21b8fd8f14 ("MIPS: seccomp: Handle indirect system calls
> (o32)"), syscall_get_arguments() attempts to handle o32 indirect syscall
> arguments by incrementing both the start argument number and the number
> of arguments to fetch. However only the start argument number needs to
> be incremented. The number of arguments does not change, they're just
> shifted up by one, and in fact the output array is provided by the
> caller and is likely only n entries long, so reading more arguments
> overflows the output buffer.
[...]
> diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
> index 6499d93ae68d..47bc45a67e9b 100644
> --- a/arch/mips/include/asm/syscall.h
> +++ b/arch/mips/include/asm/syscall.h
> @@ -101,10 +101,8 @@ static inline void syscall_get_arguments(struct task_struct *task,
> /* O32 ABI syscall() - Either 64-bit with O32 or 32-bit */
> if ((config_enabled(CONFIG_32BIT) ||
> test_tsk_thread_flag(task, TIF_32BIT_REGS)) &&
> - (regs->regs[2] == __NR_syscall)) {
> + (regs->regs[2] == __NR_syscall))
> i++;
> - n++;
> - }
>
> while (n--)
> ret |= mips_get_syscall_arg(args++, task, regs, i++);
What I think it really needs to do is to *decrease* the number of
arguments, as we're throwing the syscall number away as not an argument to
itself. So this looks like a typo to me, the expression was meant to be
`n--' rather than `n++'. With the number of arguments unchanged, as in
your proposed change, we're still reaching one word too far.
Maciej
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