[PATCH] net: sched: sch: Bounds check priority

[PATCH] net: sched: sch: Bounds check priority

[Kees Cook]

Nothing was explicitly bounds checking the priority index used to access
clpriop[]. WARN and bail out early if it's pathological. Seen with GCC 13:

../net/sched/sch_htb.c: In function 'htb_activate_prios':
../net/sched/sch_htb.c:437:44: warning: array subscript [0, 31] is outside array bounds of 'struct htb_prio[8]' [-Warray-bounds=]
  437 |                         if (p->inner.clprio[prio].feed.rb_node)
      |                             ~~~~~~~~~~~~~~~^~~~~~
../net/sched/sch_htb.c:131:41: note: while referencing 'clprio'
  131 |                         struct htb_prio clprio[TC_HTB_NUMPRIO];
      |                                         ^~~~~~

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 net/sched/sch_htb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index f46643850df8..cc28e41fb745 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -431,7 +431,10 @@ static void htb_activate_prios(struct htb_sched *q, struct htb_class *cl)
 	while (cl->cmode == HTB_MAY_BORROW && p && mask) {
 		m = mask;
 		while (m) {
-			int prio = ffz(~m);
+			unsigned int prio = ffz(~m);
+
+			if (WARN_ON_ONCE(prio > ARRAY_SIZE(p->inner.clprio)))
+				break;
 			m &= ~(1 << prio);
 
 			if (p->inner.clprio[prio].feed.rb_node)
-- 
2.34.1

Re: [PATCH] net: sched: sch: Bounds check priority

[Simon Horman]

On Fri, Jan 27, 2023 at 02:40:37PM -0800, Kees Cook wrote:
> Nothing was explicitly bounds checking the priority index used to access
> clpriop[]. WARN and bail out early if it's pathological. Seen with GCC 13:
> 
> ../net/sched/sch_htb.c: In function 'htb_activate_prios':
> ../net/sched/sch_htb.c:437:44: warning: array subscript [0, 31] is outside array bounds of 'struct htb_prio[8]' [-Warray-bounds=]
>   437 |                         if (p->inner.clprio[prio].feed.rb_node)
>       |                             ~~~~~~~~~~~~~~~^~~~~~
> ../net/sched/sch_htb.c:131:41: note: while referencing 'clprio'
>   131 |                         struct htb_prio clprio[TC_HTB_NUMPRIO];
>       |                                         ^~~~~~
> 

...

> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  net/sched/sch_htb.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

I'm not sure what will happen if we hit the 'break' case.
But I also think that warning and bailing out is an improvement on whatever
happens now if that scenario is hit.

Reviewed-by: Simon Horman <simon.horman@corigine.com>

> diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
> index f46643850df8..cc28e41fb745 100644
> --- a/net/sched/sch_htb.c
> +++ b/net/sched/sch_htb.c
> @@ -431,7 +431,10 @@ static void htb_activate_prios(struct htb_sched *q, struct htb_class *cl)
>  	while (cl->cmode == HTB_MAY_BORROW && p && mask) {
>  		m = mask;
>  		while (m) {
> -			int prio = ffz(~m);
> +			unsigned int prio = ffz(~m);
> +
> +			if (WARN_ON_ONCE(prio > ARRAY_SIZE(p->inner.clprio)))
> +				break;
>  			m &= ~(1 << prio);
>  
>  			if (p->inner.clprio[prio].feed.rb_node)
> -- 
> 2.34.1
> 

Re: [PATCH] net: sched: sch: Bounds check priority

[Cong Wang]

On Fri, Jan 27, 2023 at 02:40:37PM -0800, Kees Cook wrote:
> Nothing was explicitly bounds checking the priority index used to access
> clpriop[]. WARN and bail out early if it's pathological. Seen with GCC 13:
> 
> ../net/sched/sch_htb.c: In function 'htb_activate_prios':
> ../net/sched/sch_htb.c:437:44: warning: array subscript [0, 31] is outside array bounds of 'struct htb_prio[8]' [-Warray-bounds=]
>   437 |                         if (p->inner.clprio[prio].feed.rb_node)
>       |                             ~~~~~~~~~~~~~~~^~~~~~
> ../net/sched/sch_htb.c:131:41: note: while referencing 'clprio'
>   131 |                         struct htb_prio clprio[TC_HTB_NUMPRIO];
>       |                                         ^~~~~~

Reviewed-by: Cong Wang <cong.wang@bytedance.com>

We already have a check in htb_change_class():

2056                 if ((cl->prio = hopt->prio) >= TC_HTB_NUMPRIO)
2057                         cl->prio = TC_HTB_NUMPRIO - 1;

so this patch is just to make GCC 13 happy.

Thanks.

Re: [PATCH] net: sched: sch: Bounds check priority

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by Paolo Abeni <pabeni@redhat.com>:

On Fri, 27 Jan 2023 14:40:37 -0800 you wrote:
> Nothing was explicitly bounds checking the priority index used to access
> clpriop[]. WARN and bail out early if it's pathological. Seen with GCC 13:
> 
> ../net/sched/sch_htb.c: In function 'htb_activate_prios':
> ../net/sched/sch_htb.c:437:44: warning: array subscript [0, 31] is outside array bounds of 'struct htb_prio[8]' [-Warray-bounds=]
>   437 |                         if (p->inner.clprio[prio].feed.rb_node)
>       |                             ~~~~~~~~~~~~~~~^~~~~~
> ../net/sched/sch_htb.c:131:41: note: while referencing 'clprio'
>   131 |                         struct htb_prio clprio[TC_HTB_NUMPRIO];
>       |                                         ^~~~~~
> 
> [...]

Here is the summary with links:
  - net: sched: sch: Bounds check priority
    https://git.kernel.org/netdev/net/c/de5ca4c3852f

You are awesome, thank you!
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