Re: The disappearing sys_call_table export.

[Terje Malmedal]

[Arjan van de Ven]
> On Sat, 2003-05-10 at 16:38, Ahmed Masud wrote:
>> Case in point, I wrote a security module for Linux that overrides _all_
>> 237 systemcalls to audit and control the use of the system calls on a per
>> uid basis.  (i.e. if the user was actually allowed to make the system call
>> or not) and return -EPERM or jump to system call proper.

> I'm pretty sure that auditing by your module can easily be avoided.

> examle: pseudocode for the unlink syscall

> long your_wrapped_syscall(char *userfilename)
> {
>     char kernelpointer[something];
>     copy_from_user(kernelpointer, usefilename, ...);
>     audit_log(kernelpointer);
>     return original_syscall(userfilename);
> }

> now.... the original syscall does ANOTHER copy_from_user().
> Eg I can easily fool your logging by having a second thread change the
> filename between the time your code copies it and the time the original
> syscall copies it again. The chances of getting the timing right are 50%
> at least (been there done that ;)

> The only solution for this is to check/audit/log things after the ONE
> copy. Eg not by overriding the syscall but inside the syscall.

just replace 
     return original_syscall(userfilename);
with
     return original_syscall(kernelpointer);

-- 
 - Terje
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