Re: [PATCH v2 1/2] auditsc: audit_krule mask accesses need bounds checking

On Wednesday, May 28, 2014 10:43:57 PM Eric Paris wrote: > On Wed, 2014-05-28 at 19:27 -0700, Andy Lutomirski wrote: > > On Wed, May 28, 2014 at 7:23 PM, Eric Paris <eparis(a)redhat.com&gt; wrote: > > > On Wed, 2014-05-28 at 18:44 -0700, Andy Lutomirski wrote: > > >> Fixes an easy DoS and possible information disclosure. > > >> > > >> This does nothing about the broken state of x32 auditing. > > >> > > >> Cc: stable(a)vger.kernel.org > > >> Signed-off-by: Andy Lutomirski <luto(a)amacapital.net&gt; > > >> --- > > >> > > >> kernel/auditsc.c | 27 ++++++++++++++++++--------- > > >> 1 file changed, 18 insertions(+), 9 deletions(-) > > >> > > >> diff --git a/kernel/auditsc.c b/kernel/auditsc.c > > >> index f251a5e..7ccd9db 100644 > > >> --- a/kernel/auditsc.c > > >> +++ b/kernel/auditsc.c > > >> @@ -728,6 +728,22 @@ static enum audit_state audit_filter_task(struct > > >> task_struct *tsk, char **key)> >> > > >> return AUDIT_BUILD_CONTEXT; > > >> } > > >> > > >> +static bool audit_in_mask(const struct audit_krule *rule, unsigned > > >> long val) +{ > > >> + int word, bit; > > >> + > > >> + if (val > 0xffffffff) > > >> + return false; > > > > > > Why is this necessary? > > > > To avoid an integer overflow. Admittedly, this particular overflow > > won't cause a crash, but it will cause incorrect results. So, what is the effect of this patch? Does it hide the syscall from the audit system? Does it fail the syscall?

> You know this code pre-dates git? I admit, I'm shocked no one ever > noticed it before! This is ANCIENT. And clearly broken. > > I'll likely ask Richard to add a WARN_ONCE() in both this place, and > below in word > AUDIT_BITMASK_SIZE so we might know if we ever need a > larger bitmask to store syscall numbers.... We need absolute guarantees. Either its auditable or prevented - always.

-Steve