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Message-ID: <CAGXu5jJBnjvY3qRmVo23bL6jJXfRB9+o=-pSg9UGEr4tfeBwzQ@mail.gmail.com>
Date: Wed, 22 Mar 2017 12:30:39 -0700
From: Kees Cook <keescook@...omium.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Jakub Kicinski <jakub.kicinski@...ronome.com>, Viresh Kumar <viresh.kumar@...aro.org>,
Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
Dmitry Vyukov <dvyukov@...gle.com>, Olof Johansson <olof@...om.net>,
Josh Poimboeuf <jpoimboe@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 6/6] refcount: Check bad states with CHECK_DATA_CORRUPTION
On Mon, Mar 6, 2017 at 11:09 AM, Kees Cook <keescook@...omium.org> wrote:
> This converts from WARN() to CHECK_DATA_CORRUPTION() (so that system
> builders can choose between WARN and BUG). Additionally moves refcount_t
> sanity-check conditionals into regular function flow.
>
> Now when built with CONFIG_BUG_ON_DATA_CORRUPTION, the LKDTM REFCOUNT_*
> tests correctly kill offending processes.
Any feedback on this change? I'd like to get this and the prior
patches into -next soon for more testing.
-Kees
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> lib/refcount.c | 33 +++++++++++++++++++++------------
> 1 file changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/lib/refcount.c b/lib/refcount.c
> index 1d33366189d1..54aff1e0582f 100644
> --- a/lib/refcount.c
> +++ b/lib/refcount.c
> @@ -37,6 +37,13 @@
> #include <linux/refcount.h>
> #include <linux/bug.h>
>
> +/*
> + * CHECK_DATA_CORRUPTION() is defined with __must_check, but we have a
> + * couple places where we want to report a condition that has already
> + * been checked, so this lets us cheat __must_check.
> + */
> +#define REFCOUNT_CHECK(cond, str) unlikely(CHECK_DATA_CORRUPTION(cond, str))
> +
> bool refcount_add_not_zero(unsigned int i, refcount_t *r)
> {
> unsigned int old, new, val = atomic_read(&r->refs);
> @@ -58,7 +65,8 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
> val = old;
> }
>
> - WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
> + REFCOUNT_CHECK(new == UINT_MAX,
> + "refcount_t: add saturated; leaking memory.\n");
>
> return true;
> }
> @@ -66,7 +74,8 @@ EXPORT_SYMBOL_GPL(refcount_add_not_zero);
>
> void refcount_add(unsigned int i, refcount_t *r)
> {
> - WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
> + REFCOUNT_CHECK(!refcount_add_not_zero(i, r),
> + "refcount_t: addition on 0; use-after-free.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_add);
>
> @@ -97,7 +106,8 @@ bool refcount_inc_not_zero(refcount_t *r)
> val = old;
> }
>
> - WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
> + REFCOUNT_CHECK(new == UINT_MAX,
> + "refcount_t: inc saturated; leaking memory.\n");
>
> return true;
> }
> @@ -111,7 +121,8 @@ EXPORT_SYMBOL_GPL(refcount_inc_not_zero);
> */
> void refcount_inc(refcount_t *r)
> {
> - WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
> + REFCOUNT_CHECK(!refcount_inc_not_zero(r),
> + "refcount_t: increment on 0; use-after-free.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_inc);
>
> @@ -124,10 +135,9 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)
> return false;
>
> new = val - i;
> - if (new > val) {
> - WARN(new > val, "refcount_t: underflow; use-after-free.\n");
> + if (REFCOUNT_CHECK(new > val,
> + "refcount_t: sub underflow; use-after-free.\n"))
> return false;
> - }
>
> old = atomic_cmpxchg_release(&r->refs, val, new);
> if (old == val)
> @@ -164,7 +174,8 @@ EXPORT_SYMBOL_GPL(refcount_dec_and_test);
>
> void refcount_dec(refcount_t *r)
> {
> - WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
> + REFCOUNT_CHECK(refcount_dec_and_test(r),
> + "refcount_t: decrement hit 0; leaking memory.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_dec);
>
> @@ -203,10 +214,9 @@ bool refcount_dec_not_one(refcount_t *r)
> return false;
>
> new = val - 1;
> - if (new > val) {
> - WARN(new > val, "refcount_t: underflow; use-after-free.\n");
> + if (REFCOUNT_CHECK(new > val,
> + "refcount_t: dec underflow; use-after-free.\n"))
> return true;
> - }
>
> old = atomic_cmpxchg_release(&r->refs, val, new);
> if (old == val)
> @@ -264,4 +274,3 @@ bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
> return true;
> }
> EXPORT_SYMBOL_GPL(refcount_dec_and_lock);
> -
> --
> 2.7.4
>
--
Kees Cook
Pixel Security
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