From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Paris Subject: Re: [PATCH v2 1/2] auditsc: audit_krule mask accesses need bounds checking Date: Wed, 28 May 2014 22:43:57 -0400 Message-ID: <1401331437.13555.38.camel@localhost> References: <833bd6cb411ad1d4e293629c6c34c4abca27a840.1401327752.git.luto@amacapital.net> <1401330205.13555.29.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: stable-owner@vger.kernel.org To: Andy Lutomirski Cc: Philipp Kern , "H. Peter Anvin" , "linux-kernel@vger.kernel.org" , "H. J. Lu" , "security@kernel.org" , Greg Kroah-Hartman , linux-audit@redhat.com, stable@vger.kernel.org List-Id: linux-audit@redhat.com On Wed, 2014-05-28 at 19:27 -0700, Andy Lutomirski wrote: > On Wed, May 28, 2014 at 7:23 PM, Eric Paris 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@vger.kernel.org > >> Signed-off-by: Andy Lutomirski > >> --- > >> 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. 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.... It'd be nice if lib had a efficient bitmask implementation... > > > >> + > >> + word = AUDIT_WORD(val); > >> + if (word >= AUDIT_BITMASK_SIZE) > >> + return false; > > > > Since this covers it and it extensible... > > > >> + > >> + bit = AUDIT_BIT(val); > >> + > >> + return rule->mask[word] & bit; > > > > Returning an int as a bool creates worse code than just returning the > > int. (although in this case if the compiler chooses to inline it might > > be smart enough not to actually convert this int to a bool and make > > worse assembly...) I'd suggest the function here return an int. bools > > usually make the assembly worse... > > I'm ambivalent. The right assembly would use flags on x86, not an int > or a bool, and I don't know what the compiler will do. Also, clearly X86_X32 was implemented without audit support, so we shouldn't config it in. What do you think of this? diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 25d2c6f..fa852e2 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -129,7 +129,7 @@ config X86 select HAVE_IRQ_EXIT_ON_IRQ_STACK if X86_64 select HAVE_CC_STACKPROTECTOR select GENERIC_CPU_AUTOPROBE - select HAVE_ARCH_AUDITSYSCALL + select HAVE_ARCH_AUDITSYSCALL if !X86_X32 config INSTRUCTION_DECODER def_bool y