diff mbox series

[v2,1/1] net/sched: cls_u32: Fix reference counter leak leading to overflow

Message ID 20230608072903.3404438-1-lee@kernel.org
State New
Headers
Series [v2,1/1] net/sched: cls_u32: Fix reference counter leak leading to overflow |

Commit Message

Lee Jones June 8, 2023, 7:29 a.m. UTC 
  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>
---
v1 -> v2:
  - Instead of decrementing the refcnt in the error path, move the
    point of failure up above the section which increments it.

net/sched/cls_u32.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

Comments

Jamal Hadi Salim June 8, 2023, 4:40 p.m. UTC | #1 
On Thu, Jun 8, 2023 at 3:47 AM Lee Jones <lee@kernel.org> wrote:
>
> On Thu, 08 Jun 2023, Eric Dumazet wrote:
>
> > On Thu, Jun 8, 2023 at 9:29 AM Lee Jones <lee@kernel.org> wrote:
> > >
> > > 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>
> > > ---
> >
> > Thanks Lee !
>
> No problem.  Thanks for your help.
>
> > Reviewed-by: Eric Dumazet <edumazet@google.com>

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

cheers,
jamal

> --
> Lee Jones [李琼斯]
Lee Jones June 8, 2023, 5:58 p.m. UTC | #2 
On Thu, 08 Jun 2023, Jamal Hadi Salim wrote:

> On Thu, Jun 8, 2023 at 3:47 AM Lee Jones <lee@kernel.org> wrote:
> >
> > On Thu, 08 Jun 2023, Eric Dumazet wrote:
> >
> > > On Thu, Jun 8, 2023 at 9:29 AM Lee Jones <lee@kernel.org> wrote:
> > > >
> > > > 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>
> > > > ---
> > >
> > > Thanks Lee !
> >
> > No problem.  Thanks for your help.
> >
> > > Reviewed-by: Eric Dumazet <edumazet@google.com>
> 
> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

Thanks Jamal.
patchwork-bot+netdevbpf@kernel.org June 9, 2023, 10:50 a.m. UTC | #3 
Hello:

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

On Thu,  8 Jun 2023 08:29:03 +0100 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [v2,1/1] net/sched: cls_u32: Fix reference counter leak leading to overflow
    https://git.kernel.org/netdev/net/c/04c55383fa56

You are awesome, thank you!
diff mbox series

Patch

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 4e2e269f121f8..d15d50de79802 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -718,13 +718,19 @@  static int u32_set_parms(struct net *net, struct tcf_proto *tp,
 			 struct nlattr *est, u32 flags, u32 fl_flags,
 			 struct netlink_ext_ack *extack)
 {
-	int err;
+	int err, ifindex = -1;
 
 	err = tcf_exts_validate_ex(net, tp, tb, est, &n->exts, flags,
 				   fl_flags, extack);
 	if (err < 0)
 		return err;
 
+	if (tb[TCA_U32_INDEV]) {
+		ifindex = tcf_change_indev(net, tb[TCA_U32_INDEV], extack);
+		if (ifindex < 0)
+			return -EINVAL;
+	}
+
 	if (tb[TCA_U32_LINK]) {
 		u32 handle = nla_get_u32(tb[TCA_U32_LINK]);
 		struct tc_u_hnode *ht_down = NULL, *ht_old;
@@ -759,13 +765,9 @@  static int u32_set_parms(struct net *net, struct tcf_proto *tp,
 		tcf_bind_filter(tp, &n->res, base);
 	}
 
-	if (tb[TCA_U32_INDEV]) {
-		int ret;
-		ret = tcf_change_indev(net, tb[TCA_U32_INDEV], extack);
-		if (ret < 0)
-			return -EINVAL;
-		n->ifindex = ret;
-	}
+	if (ifindex >= 0)
+		n->ifindex = ifindex;
+
 	return 0;
 }