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tcp: take care of truncations done by sk_filter() 

commit ac6e780070e30e4c35bd395acfe9191e6268bdd3 upstream.

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: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Eric Dumazet 2016-11-10 13:12:35 -08:00 committed by syphyr
parent 101d8a32fc
commit 8222a79cb5
5 changed files with 33 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/filter.h
View File

@ -36,7 +36,11 @@ static inline unsigned int sk_filter_len(const struct sk_filter *fp)
return fp->len * sizeof(struct sock_filter) + sizeof(*fp);
}
extern 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);
}
extern unsigned int sk_run_filter(const struct sk_buff *skb,
const struct sock_filter *filter);
extern int sk_unattached_filter_create(struct sk_filter **pfp,

1
include/net/tcp.h
View File

@ -1044,6 +1044,7 @@ static inline void tcp_prequeue_init(struct tcp_sock *tp)
}
extern 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

@ -67,9 +67,10 @@ static inline void *load_pointer(const struct sk_buff *skb, int k,
}
/**
* 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 filter code and then cut skb->data to correct size returned by
* sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
@ -78,7 +79,7 @@ static inline void *load_pointer(const struct sk_buff *skb, int k,
* 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;
@ -99,14 +100,13 @@ int sk_filter(struct sock *sk, struct sk_buff *skb)
filter = rcu_dereference(sk->sk_filter);
if (filter) {
unsigned int pkt_len = SK_RUN_FILTER(filter, 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);
/**
* sk_run_filter - run a filter on a socket

19
net/ipv4/tcp_ipv4.c
View File

@ -1960,6 +1960,21 @@ 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
*/
@ -2022,8 +2037,10 @@ process:
goto discard_and_relse;
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

@ -1341,7 +1341,7 @@ static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
goto discard;
#endif
if (sk_filter(sk, skb))
if (tcp_filter(sk, skb))
goto discard;
/*
@ -1512,8 +1512,10 @@ process:
if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, 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;