[PATCH net] net/sched: cls_fw: Fix improper refcount update leads to use-after-free

[PATCH net] net/sched: cls_fw: Fix improper refcount update leads to use-after-free

[jhs]

From: M A Ramdhan <ramdhan@starlabs.sg>

In the event of a failure in tcf_change_indev(), fw_set_parms() will
immediately return an error after incrementing or decrementing
reference counter in tcf_bind_filter().  If attacker can control
reference counter to zero and make reference freed, leading to
use after free.

In order to prevent this, move the point of possible failure above the
point where the TC_FW_CLASSID is handled.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: M A Ramdhan <ramdhan@starlabs.sg>
Signed-off-by: M A Ramdhan <ramdhan@starlabs.sg>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 net/sched/cls_fw.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index ae9439a6c56c..8641f8059317 100644
--- a/net/sched/cls_fw.c
+++ b/net/sched/cls_fw.c
@@ -212,11 +212,6 @@ static int fw_set_parms(struct net *net, struct tcf_proto *tp,
 	if (err < 0)
 		return err;
 
-	if (tb[TCA_FW_CLASSID]) {
-		f->res.classid = nla_get_u32(tb[TCA_FW_CLASSID]);
-		tcf_bind_filter(tp, &f->res, base);
-	}
-
 	if (tb[TCA_FW_INDEV]) {
 		int ret;
 		ret = tcf_change_indev(net, tb[TCA_FW_INDEV], extack);
@@ -233,6 +228,11 @@ static int fw_set_parms(struct net *net, struct tcf_proto *tp,
 	} else if (head->mask != 0xFFFFFFFF)
 		return err;
 
+	if (tb[TCA_FW_CLASSID]) {
+		f->res.classid = nla_get_u32(tb[TCA_FW_CLASSID]);
+		tcf_bind_filter(tp, &f->res, base);
+	}
+
 	return 0;
 }
 
-- 
2.34.1

Re: [PATCH net] net/sched: cls_fw: Fix improper refcount update leads to use-after-free

[Pedro Tammela]

On 05/07/2023 13:15, jhs@mojatatu.com wrote:
> From: M A Ramdhan <ramdhan@starlabs.sg>
> 
> In the event of a failure in tcf_change_indev(), fw_set_parms() will
> immediately return an error after incrementing or decrementing
> reference counter in tcf_bind_filter().  If attacker can control
> reference counter to zero and make reference freed, leading to
> use after free.
> 
> In order to prevent this, move the point of possible failure above the
> point where the TC_FW_CLASSID is handled.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: M A Ramdhan <ramdhan@starlabs.sg>
> Signed-off-by: M A Ramdhan <ramdhan@starlabs.sg>
> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

LGTM,

Reviewed-by: Pedro Tammela <pctammela@mojatatu.com>

> ---
>   net/sched/cls_fw.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
> index ae9439a6c56c..8641f8059317 100644
> --- a/net/sched/cls_fw.c
> +++ b/net/sched/cls_fw.c
> @@ -212,11 +212,6 @@ static int fw_set_parms(struct net *net, struct tcf_proto *tp,
>   	if (err < 0)
>   		return err;
>   
> -	if (tb[TCA_FW_CLASSID]) {
> -		f->res.classid = nla_get_u32(tb[TCA_FW_CLASSID]);
> -		tcf_bind_filter(tp, &f->res, base);
> -	}
> -
>   	if (tb[TCA_FW_INDEV]) {
>   		int ret;
>   		ret = tcf_change_indev(net, tb[TCA_FW_INDEV], extack);
> @@ -233,6 +228,11 @@ static int fw_set_parms(struct net *net, struct tcf_proto *tp,
>   	} else if (head->mask != 0xFFFFFFFF)
>   		return err;
>   
> +	if (tb[TCA_FW_CLASSID]) {
> +		f->res.classid = nla_get_u32(tb[TCA_FW_CLASSID]);
> +		tcf_bind_filter(tp, &f->res, base);
> +	}
> +
>   	return 0;
>   }
>   

Re: [PATCH net] net/sched: cls_fw: Fix improper refcount update leads to use-after-free

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed,  5 Jul 2023 12:15:30 -0400 you wrote:
> From: M A Ramdhan <ramdhan@starlabs.sg>
> 
> In the event of a failure in tcf_change_indev(), fw_set_parms() will
> immediately return an error after incrementing or decrementing
> reference counter in tcf_bind_filter().  If attacker can control
> reference counter to zero and make reference freed, leading to
> use after free.
> 
> [...]

Here is the summary with links:
  - [net] net/sched: cls_fw: Fix improper refcount update leads to use-after-free
    https://git.kernel.org/netdev/net/c/0323bce598ee

You are awesome, thank you!
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