| Message ID | 20210118055920.82516-1-kuniyu@amazon.co.jp |
|---|---|
| State | New |
| Headers | show |
| Series | [net] tcp: Fix potential use-after-free due to double kfree(). | expand |
On Mon, 18 Jan 2021 14:59:20 +0900 Kuniyuki Iwashima wrote: > Receiving ACK with a valid SYN cookie, cookie_v4_check() allocates struct > request_sock and then can allocate inet_rsk(req)->ireq_opt. After that, > tcp_v4_syn_recv_sock() allocates struct sock and copies ireq_opt to > inet_sk(sk)->inet_opt. Normally, tcp_v4_syn_recv_sock() inserts the full > socket into ehash and sets NULL to ireq_opt. Otherwise, > tcp_v4_syn_recv_sock() has to reset inet_opt by NULL and free the full > socket. > > The commit 01770a1661657 ("tcp: fix race condition when creating child > sockets from syncookies") added a new path, in which more than one cores > create full sockets for the same SYN cookie. Currently, the core which > loses the race frees the full socket without resetting inet_opt, resulting > in that both sock_put() and reqsk_put() call kfree() for the same memory: > > sock_put > sk_free > __sk_free > sk_destruct > __sk_destruct > sk->sk_destruct/inet_sock_destruct > kfree(rcu_dereference_protected(inet->inet_opt, 1)); > > reqsk_put > reqsk_free > __reqsk_free > req->rsk_ops->destructor/tcp_v4_reqsk_destructor > kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1)); > > Calling kmalloc() between the double kfree() can lead to use-after-free, so > this patch fixes it by setting NULL to inet_opt before sock_put(). > > As a side note, this kind of issue does not happen for IPv6. This is > because tcp_v6_syn_recv_sock() clones both ipv6_opt and pktopts which > correspond to ireq_opt in IPv4. > > Fixes: 01770a166165 ("tcp: fix race condition when creating child sockets from syncookies") > CC: Ricardo Dias <rdias@singlestore.com> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp> > Reviewed-by: Benjamin Herrenschmidt <benh@amazon.com> Ricardo, Eric, any reason this was written this way? > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c > index 58207c7769d0..87eb614dab27 100644 > --- a/net/ipv4/tcp_ipv4.c > +++ b/net/ipv4/tcp_ipv4.c > @@ -1595,6 +1595,8 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb, > tcp_move_syn(newtp, req); > ireq->ireq_opt = NULL; > } else { > + newinet->inet_opt = NULL; > + > if (!req_unhash && found_dup_sk) { > /* This code path should only be executed in the > * syncookie case only > @@ -1602,8 +1604,6 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb, > bh_unlock_sock(newsk); > sock_put(newsk); > newsk = NULL; > - } else { > - newinet->inet_opt = NULL; > } > } > return newsk;
On Wed, Jan 20, 2021 at 2:17 AM Jakub Kicinski <kuba@kernel.org> wrote: > > On Mon, 18 Jan 2021 14:59:20 +0900 Kuniyuki Iwashima wrote: > > Receiving ACK with a valid SYN cookie, cookie_v4_check() allocates struct > > request_sock and then can allocate inet_rsk(req)->ireq_opt. After that, > > tcp_v4_syn_recv_sock() allocates struct sock and copies ireq_opt to > > inet_sk(sk)->inet_opt. Normally, tcp_v4_syn_recv_sock() inserts the full > > socket into ehash and sets NULL to ireq_opt. Otherwise, > > tcp_v4_syn_recv_sock() has to reset inet_opt by NULL and free the full > > socket. > > > > The commit 01770a1661657 ("tcp: fix race condition when creating child > > sockets from syncookies") added a new path, in which more than one cores > > create full sockets for the same SYN cookie. Currently, the core which > > loses the race frees the full socket without resetting inet_opt, resulting > > in that both sock_put() and reqsk_put() call kfree() for the same memory: > > > > sock_put > > sk_free > > __sk_free > > sk_destruct > > __sk_destruct > > sk->sk_destruct/inet_sock_destruct > > kfree(rcu_dereference_protected(inet->inet_opt, 1)); > > > > reqsk_put > > reqsk_free > > __reqsk_free > > req->rsk_ops->destructor/tcp_v4_reqsk_destructor > > kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1)); > > > > Calling kmalloc() between the double kfree() can lead to use-after-free, so > > this patch fixes it by setting NULL to inet_opt before sock_put(). > > > > As a side note, this kind of issue does not happen for IPv6. This is > > because tcp_v6_syn_recv_sock() clones both ipv6_opt and pktopts which > > correspond to ireq_opt in IPv4. > > > > Fixes: 01770a166165 ("tcp: fix race condition when creating child sockets from syncookies") > > CC: Ricardo Dias <rdias@singlestore.com> > > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp> > > Reviewed-by: Benjamin Herrenschmidt <benh@amazon.com> > > Ricardo, Eric, any reason this was written this way? Well, I guess that was a plain bug. IPv4 options are not used often I think. Reviewed-by: Eric Dumazet <edumazet@google.com>
On Wed, 20 Jan 2021 14:07:35 +0100 Eric Dumazet wrote: > On Wed, Jan 20, 2021 at 2:17 AM Jakub Kicinski <kuba@kernel.org> wrote: > > On Mon, 18 Jan 2021 14:59:20 +0900 Kuniyuki Iwashima wrote: > > > Receiving ACK with a valid SYN cookie, cookie_v4_check() allocates struct > > > request_sock and then can allocate inet_rsk(req)->ireq_opt. After that, > > > tcp_v4_syn_recv_sock() allocates struct sock and copies ireq_opt to > > > inet_sk(sk)->inet_opt. Normally, tcp_v4_syn_recv_sock() inserts the full > > > socket into ehash and sets NULL to ireq_opt. Otherwise, > > > tcp_v4_syn_recv_sock() has to reset inet_opt by NULL and free the full > > > socket. > > > > > > The commit 01770a1661657 ("tcp: fix race condition when creating child > > > sockets from syncookies") added a new path, in which more than one cores > > > create full sockets for the same SYN cookie. Currently, the core which > > > loses the race frees the full socket without resetting inet_opt, resulting > > > in that both sock_put() and reqsk_put() call kfree() for the same memory: > > > > > > sock_put > > > sk_free > > > __sk_free > > > sk_destruct > > > __sk_destruct > > > sk->sk_destruct/inet_sock_destruct > > > kfree(rcu_dereference_protected(inet->inet_opt, 1)); > > > > > > reqsk_put > > > reqsk_free > > > __reqsk_free > > > req->rsk_ops->destructor/tcp_v4_reqsk_destructor > > > kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1)); > > > > > > Calling kmalloc() between the double kfree() can lead to use-after-free, so > > > this patch fixes it by setting NULL to inet_opt before sock_put(). > > > > > > As a side note, this kind of issue does not happen for IPv6. This is > > > because tcp_v6_syn_recv_sock() clones both ipv6_opt and pktopts which > > > correspond to ireq_opt in IPv4. > > > > > > Fixes: 01770a166165 ("tcp: fix race condition when creating child sockets from syncookies") > > > CC: Ricardo Dias <rdias@singlestore.com> > > > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp> > > > Reviewed-by: Benjamin Herrenschmidt <benh@amazon.com> > > > > Ricardo, Eric, any reason this was written this way? > > Well, I guess that was a plain bug. > > IPv4 options are not used often I think. I see. > Reviewed-by: Eric Dumazet <edumazet@google.com> Applied, thank you!
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 58207c7769d0..87eb614dab27 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1595,6 +1595,8 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb, tcp_move_syn(newtp, req); ireq->ireq_opt = NULL; } else { + newinet->inet_opt = NULL; + if (!req_unhash && found_dup_sk) { /* This code path should only be executed in the * syncookie case only @@ -1602,8 +1604,6 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb, bh_unlock_sock(newsk); sock_put(newsk); newsk = NULL; - } else { - newinet->inet_opt = NULL; } } return newsk;
Receiving ACK with a valid SYN cookie, cookie_v4_check() allocates struct request_sock and then can allocate inet_rsk(req)->ireq_opt. After that, tcp_v4_syn_recv_sock() allocates struct sock and copies ireq_opt to inet_sk(sk)->inet_opt. Normally, tcp_v4_syn_recv_sock() inserts the full socket into ehash and sets NULL to ireq_opt. Otherwise, tcp_v4_syn_recv_sock() has to reset inet_opt by NULL and free the full socket. The commit 01770a1661657 ("tcp: fix race condition when creating child sockets from syncookies") added a new path, in which more than one cores create full sockets for the same SYN cookie. Currently, the core which loses the race frees the full socket without resetting inet_opt, resulting in that both sock_put() and reqsk_put() call kfree() for the same memory: sock_put sk_free __sk_free sk_destruct __sk_destruct sk->sk_destruct/inet_sock_destruct kfree(rcu_dereference_protected(inet->inet_opt, 1)); reqsk_put reqsk_free __reqsk_free req->rsk_ops->destructor/tcp_v4_reqsk_destructor kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1)); Calling kmalloc() between the double kfree() can lead to use-after-free, so this patch fixes it by setting NULL to inet_opt before sock_put(). As a side note, this kind of issue does not happen for IPv6. This is because tcp_v6_syn_recv_sock() clones both ipv6_opt and pktopts which correspond to ireq_opt in IPv4. Fixes: 01770a166165 ("tcp: fix race condition when creating child sockets from syncookies") CC: Ricardo Dias <rdias@singlestore.com> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp> Reviewed-by: Benjamin Herrenschmidt <benh@amazon.com> --- net/ipv4/tcp_ipv4.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)