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

H. Peter Anvin
2014-06-16T21:49:25Z

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