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tcp: take care of truncations done by sk_filter()

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[ Upstream commit ac6e780070 ]

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 <edumazet@google.com>
Reported-by: Marco Grassi <marco.gra@gmail.com>
Reported-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eric Dumazet
2016-11-10 13:12:35 -08:00
committed by Greg Kroah-Hartman
parent ae9e052a58
commit 225a24ae97
5 changed files with 33 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/filter.h
View File

@@ -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);

1
include/net/tcp.h
View File

@@ -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

10
net/core/filter.c
View File

@@ -52,9 +52,10 @@
#include <net/dst.h>
/**
* 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)
{

19
net/ipv4/tcp_ipv4.c
View File

@@ -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;

6
net/ipv6/tcp_ipv6.c
View File

@@ -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;