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Date: Sat, 18 Sep 2004 11:08:39 -0700 (PDT)
From: Don Lewis <truckman@FreeBSD.org>
To: gerarra@tin.it
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cc: freebsd-hackers@FreeBSD.org
Subject: Re: FreeBSD Kernel buffer overflow
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On 18 Sep, gerarra@tin.it wrote:
> Here i report a patch different from Giorgos' one. The approch is completely
> different: working on syscall_register() function in kern/kern_syscalls.c
> file.
> 
> ==============================
> 
>> cat kern_syscalls.diff
> --- kern_syscalls.c     Sat Sep 18 14:37:53 2004
> +++ kern_syscalls2.c    Sat Sep 18 14:37:53 2004
> @@ -73,6 +73,11 @@
>                                 sysent[*offset].sy_call != (sy_call_t *)lkmressys)
>                 return EEXIST;
> 
> +#if (__i386__) && (INVARIANTS)
> +       KASSERT(new_sysent->nargs >= 0 && new_sysent->nargs <= i386_SYS_ARGS,
> +               "invalid number of syscalls");
> +#endif
> +
>         *old_sysent = sysent[*offset];
>         sysent[*offset] = *new_sysent;
>         return 0;

Why panic the machine at this point?  Just refuse to install the syscall
and return an error.