linux-kernel - Re: 3.15: kernel BUG at kernel/auditsc.c:1525!

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Message-ID: <539F6646.4040605@zytor.com>
Date:	Mon, 16 Jun 2014 14:48:54 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Richard Weinberger <richard@....at>, X86 ML <x86@...nel.org>
CC:	Toralf Förster <toralf.foerster@....de>,
	Eric Paris <eparis@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 3.15: kernel BUG at kernel/auditsc.c:1525!

On 06/16/2014 02:35 PM, Andy Lutomirski wrote:
> 
> To hpa, etc:  It appears that entry_32.S is missing any call to the
> audit exit hook on the badsys path.  If I'm diagnosing this bug report
> correctly, this causes OOPSes.
> 
> The the world at large: it's increasingly apparent that no one (except
> maybe the blackhats) has ever scrutinized the syscall auditing code.
> This is two old severe bugs in the code that have probably been there
> for a long time.
> 

Yes, the audit code is a total mess.

> The bad syscall nr paths are their own incomprehensible route
> through the entry control flow.  Rearrange them to work just like
> syscalls that return -ENOSYS.

I have to admit... it sort of lends itself to a solution like this:

	/* For the 64-bit case, analogous code for 32 bits */
	movl $__NR_syscall_max+1,%ecx	# *Not* __NR_syscall_max
	cmpq %rcx,%rax
	cmovae %rcx,%rax
        movq %r10,%rcx
        call *sys_call_table(,%rax,8)

... and having an extra (invalid) system call slot in the syscall table
beyond the end instead of branching off separately.

(Note: we could use either cmova or cmovae, and either the 32- or 64-bit
form... the reason why is left as an exercise to the reader.)

	-hpa


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