[PATCH net v2] net/sched: clear actions pointer in miss cookie init fail

[PATCH net v2] net/sched: clear actions pointer in miss cookie init fail

[Pedro Tammela]

Palash reports a UAF when using a modified version of syzkaller[1].

When 'tcf_exts_miss_cookie_base_alloc()' fails in 'tcf_exts_init_ex()'
a call to 'tcf_exts_destroy()' is made to free up the tcf_exts
resources.
In flower, a call to '__fl_put()' when 'tcf_exts_init_ex()' fails is made;
Then calling 'tcf_exts_destroy()', which triggers an UAF since the
already freed tcf_exts action pointer is lingering in the struct.

Before the offending patch, this was not an issue since there was no
case where the tcf_exts action pointer could linger. Therefore, restore
the old semantic by clearing the action pointer in case of a failure to
initialize the miss_cookie.

[1] https://github.com/cmu-pasta/linux-kernel-enriched-corpus

v1->v2: Fix compilation on configs without tc actions (kernel test robot)

Fixes: 80cd22c35c90 ("net/sched: cls_api: Support hardware miss to tc action")
Reported-by: Palash Oswal <oswalpalash@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
---
 net/sched/cls_api.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 2a6b6be0811b..35785a36c802 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -3235,6 +3235,9 @@ int tcf_exts_init_ex(struct tcf_exts *exts, struct net *net, int action,
 
 err_miss_alloc:
 	tcf_exts_destroy(exts);
+#ifdef CONFIG_NET_CLS_ACT
+	exts->actions = NULL;
+#endif
 	return err;
 }
 EXPORT_SYMBOL(tcf_exts_init_ex);
-- 
2.34.1

Re: [PATCH net v2] net/sched: clear actions pointer in miss cookie init fail

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Sat, 15 Apr 2023 12:33:09 -0300 you wrote:
> Palash reports a UAF when using a modified version of syzkaller[1].
> 
> When 'tcf_exts_miss_cookie_base_alloc()' fails in 'tcf_exts_init_ex()'
> a call to 'tcf_exts_destroy()' is made to free up the tcf_exts
> resources.
> In flower, a call to '__fl_put()' when 'tcf_exts_init_ex()' fails is made;
> Then calling 'tcf_exts_destroy()', which triggers an UAF since the
> already freed tcf_exts action pointer is lingering in the struct.
> 
> [...]

Here is the summary with links:
  - [net,v2] net/sched: clear actions pointer in miss cookie init fail
    https://git.kernel.org/netdev/net/c/338469d677e5

You are awesome, thank you!
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