[PATCH 4.14] net/sched: cls_u32: Fix reference counter leak leading to overflow

[PATCH 4.14] net/sched: cls_u32: Fix reference counter leak leading to overflow

[Rishabh Bhatnagar]

From: Lee Jones <lee@kernel.org>

Upstream commit 04c55383fa5689357bcdd2c8036725a55ed632bc.

In the event of a failure in tcf_change_indev(), u32_set_parms() will
immediately return without decrementing the recently incremented
reference counter.  If this happens enough times, the counter will
rollover and the reference freed, leading to a double free which can be
used to do 'bad things'.

In order to prevent this, move the point of possible failure above the
point where the reference counter is incremented.  Also save any
meaningful return values to be applied to the return data at the
appropriate point in time.

This issue was caught with KASAN.

Fixes: 705c7091262d ("net: sched: cls_u32: no need to call tcf_exts_change for newly allocated struct")
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Rishabh Bhatnagar <risbhat@amazon.com>
---
 net/sched/cls_u32.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index fdbdcba44917..a4e01220a53a 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -774,11 +774,22 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
 			 struct nlattr *est, bool ovr)
 {
 	int err;
+#ifdef CONFIG_NET_CLS_IND
+	int ifindex = -1;
+#endif
 
 	err = tcf_exts_validate(net, tp, tb, est, &n->exts, ovr);
 	if (err < 0)
 		return err;
 
+#ifdef CONFIG_NET_CLS_IND
+	if (tb[TCA_U32_INDEV]) {
+		ifindex = tcf_change_indev(net, tb[TCA_U32_INDEV]);
+		if (ifindex < 0)
+			return -EINVAL;
+	}
+#endif
+
 	if (tb[TCA_U32_LINK]) {
 		u32 handle = nla_get_u32(tb[TCA_U32_LINK]);
 		struct tc_u_hnode *ht_down = NULL, *ht_old;
@@ -806,14 +817,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
 	}
 
 #ifdef CONFIG_NET_CLS_IND
-	if (tb[TCA_U32_INDEV]) {
-		int ret;
-		ret = tcf_change_indev(net, tb[TCA_U32_INDEV]);
-		if (ret < 0)
-			return -EINVAL;
-		n->ifindex = ret;
-	}
+	if (ifindex >= 0)
+		n->ifindex = ifindex;
 #endif
+
 	return 0;
 }
 
-- 
2.40.1

Re: [PATCH 4.14] net/sched: cls_u32: Fix reference counter leak leading to overflow

[SeongJae Park]

On Thu, 27 Jul 2023 19:15:54 +0000 Rishabh Bhatnagar <risbhat@amazon.com> wrote:

> From: Lee Jones <lee@kernel.org>
> 
> Upstream commit 04c55383fa5689357bcdd2c8036725a55ed632bc.
> 
> In the event of a failure in tcf_change_indev(), u32_set_parms() will
> immediately return without decrementing the recently incremented
> reference counter.  If this happens enough times, the counter will
> rollover and the reference freed, leading to a double free which can be
> used to do 'bad things'.
> 
> In order to prevent this, move the point of possible failure above the
> point where the reference counter is incremented.  Also save any
> meaningful return values to be applied to the return data at the
> appropriate point in time.
> 
> This issue was caught with KASAN.
> 
> Fixes: 705c7091262d ("net: sched: cls_u32: no need to call tcf_exts_change for newly allocated struct")
> Suggested-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Lee Jones <lee@kernel.org>
> Reviewed-by: Eric Dumazet <edumazet@google.com>
> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Rishabh Bhatnagar <risbhat@amazon.com>

Acked-by: SeongJae Park <sj@kernel.org>

> ---
>  net/sched/cls_u32.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index fdbdcba44917..a4e01220a53a 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -774,11 +774,22 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
>  			 struct nlattr *est, bool ovr)
>  {
>  	int err;
> +#ifdef CONFIG_NET_CLS_IND
> +	int ifindex = -1;
> +#endif
>  
>  	err = tcf_exts_validate(net, tp, tb, est, &n->exts, ovr);
>  	if (err < 0)
>  		return err;
>  
> +#ifdef CONFIG_NET_CLS_IND
> +	if (tb[TCA_U32_INDEV]) {
> +		ifindex = tcf_change_indev(net, tb[TCA_U32_INDEV]);
> +		if (ifindex < 0)
> +			return -EINVAL;
> +	}
> +#endif
> +
>  	if (tb[TCA_U32_LINK]) {
>  		u32 handle = nla_get_u32(tb[TCA_U32_LINK]);
>  		struct tc_u_hnode *ht_down = NULL, *ht_old;
> @@ -806,14 +817,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
>  	}
>  
>  #ifdef CONFIG_NET_CLS_IND
> -	if (tb[TCA_U32_INDEV]) {
> -		int ret;
> -		ret = tcf_change_indev(net, tb[TCA_U32_INDEV]);
> -		if (ret < 0)
> -			return -EINVAL;
> -		n->ifindex = ret;
> -	}
> +	if (ifindex >= 0)
> +		n->ifindex = ifindex;
>  #endif
> +
>  	return 0;

Very trivial nit: Someone might think the above new line is better not to be
added?  I don't really care, though.

>  }
>  
> -- 
> 2.40.1
> 

Thanks,
SJ

Re: [PATCH 4.14] net/sched: cls_u32: Fix reference counter leak leading to overflow

[Greg KH]

On Thu, Jul 27, 2023 at 07:15:54PM +0000, Rishabh Bhatnagar wrote:
> From: Lee Jones <lee@kernel.org>
> 
> Upstream commit 04c55383fa5689357bcdd2c8036725a55ed632bc.
> 
> In the event of a failure in tcf_change_indev(), u32_set_parms() will
> immediately return without decrementing the recently incremented
> reference counter.  If this happens enough times, the counter will
> rollover and the reference freed, leading to a double free which can be
> used to do 'bad things'.
> 
> In order to prevent this, move the point of possible failure above the
> point where the reference counter is incremented.  Also save any
> meaningful return values to be applied to the return data at the
> appropriate point in time.
> 
> This issue was caught with KASAN.
> 
> Fixes: 705c7091262d ("net: sched: cls_u32: no need to call tcf_exts_change for newly allocated struct")
> Suggested-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Lee Jones <lee@kernel.org>
> Reviewed-by: Eric Dumazet <edumazet@google.com>
> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Rishabh Bhatnagar <risbhat@amazon.com>
> ---
>  net/sched/cls_u32.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)

We need a 4.19.y backport before we can apply a 4.14.y version, as you
do not want to upgrade and have a regression.

thanks,

greg k-h