rose: limit sk_filter trim to payload
Sockets can have a filter program attached that drops or trims
incoming packets based on the filter program return value.
Rose requires data packets to have at least ROSE_MIN_LEN bytes. It
verifies this on arrival in rose_route_frame and unconditionally pulls
the bytes in rose_recvmsg. The filter can trim packets to below this
value in-between, causing pull to fail, leaving the partial header at
the time of skb_copy_datagram_msg.
Place a lower bound on the size to which sk_filter may trim packets
by introducing sk_filter_trim_cap and call this for rose packets.
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/filter.c b/net/core/filter.c
index c4b330c..e759d90 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -53,9 +53,10 @@
#include <net/sock_reuseport.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
@@ -64,7 +65,7 @@
* 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;
@@ -85,14 +86,13 @@
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)
{