| Message ID | tencent_2A17499A4FFA4D830F7D2F72A95A4ADAB308@qq.com (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: Fix potential RCU dereference issue in tcp_assign_congestion_control | expand |
Jiawei Ye <jiawei.ye@foxmail.com> wrote: > In the `tcp_assign_congestion_control` function, the `ca->flags` is > accessed after the RCU read-side critical section is unlocked. According > to RCU usage rules, this is illegal. Reusing this pointer can lead to > unpredictable behavior, including accessing memory that has been updated > or causing use-after-free issues. > > This possible bug was identified using a static analysis tool developed > by myself, specifically designed to detect RCU-related issues. > > To resolve this issue, the `rcu_read_unlock` call has been moved to the > end of the function. > > Signed-off-by: Jiawei Ye <jiawei.ye@foxmail.com> > --- > In another part of the file, `tcp_set_congestion_control` calls > `tcp_reinit_congestion_control`, ensuring that the congestion control > reinitialization process is protected by RCU. The > `tcp_reinit_congestion_control` function contains operations almost > identical to those in `tcp_assign_congestion_control`, but the former > operates under full RCU protection, whereas the latter is only partially > protected. The differing protection strategies between the two may > warrant further unification. > --- > net/ipv4/tcp_cong.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c > index 0306d257fa64..356a59d316e3 100644 > --- a/net/ipv4/tcp_cong.c > +++ b/net/ipv4/tcp_cong.c > @@ -223,13 +223,13 @@ void tcp_assign_congestion_control(struct sock *sk) > if (unlikely(!bpf_try_module_get(ca, ca->owner))) > ca = &tcp_reno; After this, ca either has module refcount incremented, so it can't go away anymore, or reno fallback was enabled (always bultin). > icsk->icsk_ca_ops = ca; > - rcu_read_unlock(); Therefore its ok to rcu unlock here.
On Fri, Sep 20, 2024 at 11:35 AM Florian Westphal <fw@strlen.de> wrote: > > Jiawei Ye <jiawei.ye@foxmail.com> wrote: > > In the `tcp_assign_congestion_control` function, the `ca->flags` is > > accessed after the RCU read-side critical section is unlocked. According > > to RCU usage rules, this is illegal. Reusing this pointer can lead to > > unpredictable behavior, including accessing memory that has been updated > > or causing use-after-free issues. > > > > This possible bug was identified using a static analysis tool developed > > by myself, specifically designed to detect RCU-related issues. > > > > To resolve this issue, the `rcu_read_unlock` call has been moved to the > > end of the function. > > > > Signed-off-by: Jiawei Ye <jiawei.ye@foxmail.com> > > --- > > In another part of the file, `tcp_set_congestion_control` calls > > `tcp_reinit_congestion_control`, ensuring that the congestion control > > reinitialization process is protected by RCU. The > > `tcp_reinit_congestion_control` function contains operations almost > > identical to those in `tcp_assign_congestion_control`, but the former > > operates under full RCU protection, whereas the latter is only partially > > protected. The differing protection strategies between the two may > > warrant further unification. > > --- > > net/ipv4/tcp_cong.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c > > index 0306d257fa64..356a59d316e3 100644 > > --- a/net/ipv4/tcp_cong.c > > +++ b/net/ipv4/tcp_cong.c > > @@ -223,13 +223,13 @@ void tcp_assign_congestion_control(struct sock *sk) > > if (unlikely(!bpf_try_module_get(ca, ca->owner))) > > ca = &tcp_reno; > > After this, ca either has module refcount incremented, so it can't > go away anymore, or reno fallback was enabled (always bultin). > > > icsk->icsk_ca_ops = ca; > > - rcu_read_unlock(); > > Therefore its ok to rcu unlock here. I agree, there is no bug here. Jiawei Ye, I guess your static analysis tool is not ready yet.
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 0306d257fa64..356a59d316e3 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -223,13 +223,13 @@ void tcp_assign_congestion_control(struct sock *sk) if (unlikely(!bpf_try_module_get(ca, ca->owner))) ca = &tcp_reno; icsk->icsk_ca_ops = ca; - rcu_read_unlock(); memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv)); if (ca->flags & TCP_CONG_NEEDS_ECN) INET_ECN_xmit(sk); else INET_ECN_dontxmit(sk); + rcu_read_unlock(); } void tcp_init_congestion_control(struct sock *sk)
In the `tcp_assign_congestion_control` function, the `ca->flags` is accessed after the RCU read-side critical section is unlocked. According to RCU usage rules, this is illegal. Reusing this pointer can lead to unpredictable behavior, including accessing memory that has been updated or causing use-after-free issues. This possible bug was identified using a static analysis tool developed by myself, specifically designed to detect RCU-related issues. To resolve this issue, the `rcu_read_unlock` call has been moved to the end of the function. Signed-off-by: Jiawei Ye <jiawei.ye@foxmail.com> --- In another part of the file, `tcp_set_congestion_control` calls `tcp_reinit_congestion_control`, ensuring that the congestion control reinitialization process is protected by RCU. The `tcp_reinit_congestion_control` function contains operations almost identical to those in `tcp_assign_congestion_control`, but the former operates under full RCU protection, whereas the latter is only partially protected. The differing protection strategies between the two may warrant further unification. --- net/ipv4/tcp_cong.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)