linux-kernel - Re: [PATCH] score: fix off-by-one index into syscall table

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Date:	Tue, 10 Jan 2012 14:40:27 +0800
From:	Eugene Teo <eugeneteo@...nel.sg>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	liqin.chen@...plusct.com, lennox.wu@...il.com,
	linux-kernel@...r.kernel.org, security@...nel.org, arnd@...db.de
Subject: Re: [PATCH] score: fix off-by-one index into syscall table

Cc'ed arnd@...db.de

ping

On Fri, Jan 6, 2012 at 9:21 PM, Dan Rosenberg <drosenberg@...curity.com> wrote:
> If the provided system call number is equal to __NR_syscalls, the
> current check will pass and a function pointer just after the system
> call table may be called, since sys_call_table is an array with total
> size __NR_syscalls.  Whether or not this is a security bug depends on
> what the compiler puts immediately after the system call table.  It's
> likely that this won't do anything bad because there is an additional
> NULL check on the syscall entry, but if there happens to be a non-NULL
> value immediately after the system call table, this may result in local
> privilege escalation.
>
> Signed-off-by: Dan Rosenberg <drosenberg@...curity.com>
> Cc: stable@...nel.org
> Cc: security@...nel.org
> ---
>  arch/score/kernel/entry.S |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/score/kernel/entry.S b/arch/score/kernel/entry.S
> index 577abba..83bb960 100644
> --- a/arch/score/kernel/entry.S
> +++ b/arch/score/kernel/entry.S
> @@ -408,7 +408,7 @@ ENTRY(handle_sys)
>        sw      r9, [r0, PT_EPC]
>
>        cmpi.c  r27, __NR_syscalls      # check syscall number
> -       bgtu    illegal_syscall
> +       bgeu    illegal_syscall
>
>        slli    r8, r27, 2              # get syscall routine
>        la      r11, sys_call_table
>
>
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