From 225a24ae97331f3b9d97c1bb97b1e30b3633bcf4 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 10 Nov 2016 13:12:35 -0800 Subject: [PATCH] tcp: take care of truncations done by sk_filter() [ Upstream commit ac6e780070e30e4c35bd395acfe9191e6268bdd3 ] With syzkaller help, Marco Grassi found a bug in TCP stack, crashing in tcp_collapse() Root cause is that sk_filter() can truncate the incoming skb, but TCP stack was not really expecting this to happen. It probably was expecting a simple DROP or ACCEPT behavior. We first need to make sure no part of TCP header could be removed. Then we need to adjust TCP_SKB_CB(skb)->end_seq Many thanks to syzkaller team and Marco for giving us a reproducer. Signed-off-by: Eric Dumazet Reported-by: Marco Grassi Reported-by: Vladis Dronov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/filter.h | 6 +++++- include/net/tcp.h | 1 + net/core/filter.c | 10 +++++----- net/ipv4/tcp_ipv4.c | 19 ++++++++++++++++++- net/ipv6/tcp_ipv6.c | 6 ++++-- 5 files changed, 33 insertions(+), 9 deletions(-) diff --git a/include/linux/filter.h b/include/linux/filter.h index 5110d4211866..ccb98b459c59 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -421,7 +421,11 @@ static inline void bpf_prog_unlock_ro(struct bpf_prog *fp) } #endif /* CONFIG_DEBUG_SET_MODULE_RONX */ -int sk_filter(struct sock *sk, struct sk_buff *skb); +int sk_filter_trim_cap(struct sock *sk, struct sk_buff *skb, unsigned int cap); +static inline int sk_filter(struct sock *sk, struct sk_buff *skb) +{ + return sk_filter_trim_cap(sk, skb, 1); +} int bpf_prog_select_runtime(struct bpf_prog *fp); void bpf_prog_free(struct bpf_prog *fp); diff --git a/include/net/tcp.h b/include/net/tcp.h index 9c3ab544d3a8..e9d7a8ef9a6d 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1156,6 +1156,7 @@ static inline void tcp_prequeue_init(struct tcp_sock *tp) } bool tcp_prequeue(struct sock *sk, struct sk_buff *skb); +int tcp_filter(struct sock *sk, struct sk_buff *skb); #undef STATE_TRACE diff --git a/net/core/filter.c b/net/core/filter.c index 75e9b2b2336d..e94355452166 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -52,9 +52,10 @@ #include /** - * sk_filter - run a packet through a socket filter + * sk_filter_trim_cap - run a packet through a socket filter * @sk: sock associated with &sk_buff * @skb: buffer to filter + * @cap: limit on how short the eBPF program may trim the packet * * Run the eBPF program and then cut skb->data to correct size returned by * the program. If pkt_len is 0 we toss packet. If skb->len is smaller @@ -63,7 +64,7 @@ * be accepted or -EPERM if the packet should be tossed. * */ -int sk_filter(struct sock *sk, struct sk_buff *skb) +int sk_filter_trim_cap(struct sock *sk, struct sk_buff *skb, unsigned int cap) { int err; struct sk_filter *filter; @@ -84,14 +85,13 @@ int sk_filter(struct sock *sk, struct sk_buff *skb) filter = rcu_dereference(sk->sk_filter); if (filter) { unsigned int pkt_len = bpf_prog_run_save_cb(filter->prog, skb); - - err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM; + err = pkt_len ? pskb_trim(skb, max(cap, pkt_len)) : -EPERM; } rcu_read_unlock(); return err; } -EXPORT_SYMBOL(sk_filter); +EXPORT_SYMBOL(sk_filter_trim_cap); static u64 __skb_get_pay_offset(u64 ctx, u64 a, u64 x, u64 r4, u64 r5) { diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index b5853cac3269..b58a38eea059 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1533,6 +1533,21 @@ bool tcp_prequeue(struct sock *sk, struct sk_buff *skb) } EXPORT_SYMBOL(tcp_prequeue); +int tcp_filter(struct sock *sk, struct sk_buff *skb) +{ + struct tcphdr *th = (struct tcphdr *)skb->data; + unsigned int eaten = skb->len; + int err; + + err = sk_filter_trim_cap(sk, skb, th->doff * 4); + if (!err) { + eaten -= skb->len; + TCP_SKB_CB(skb)->end_seq -= eaten; + } + return err; +} +EXPORT_SYMBOL(tcp_filter); + /* * From tcp_input.c */ @@ -1638,8 +1653,10 @@ process: nf_reset(skb); - if (sk_filter(sk, skb)) + if (tcp_filter(sk, skb)) goto discard_and_relse; + th = (const struct tcphdr *)skb->data; + iph = ip_hdr(skb); skb->dev = NULL; diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index fbd521fdae53..5f581616bf6a 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1214,7 +1214,7 @@ static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb) if (skb->protocol == htons(ETH_P_IP)) return tcp_v4_do_rcv(sk, skb); - if (sk_filter(sk, skb)) + if (tcp_filter(sk, skb)) goto discard; /* @@ -1438,8 +1438,10 @@ process: if (tcp_v6_inbound_md5_hash(sk, skb)) goto discard_and_relse; - if (sk_filter(sk, skb)) + if (tcp_filter(sk, skb)) goto discard_and_relse; + th = (const struct tcphdr *)skb->data; + hdr = ipv6_hdr(skb); skb->dev = NULL; -- 2.34.1