rose: limit sk_filter trim to payload

commit f4979fcea7fd36d8e2f556abef86f80e0d5af1ba upstream.

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 8eeb205f298b078ccbaa714b2d171a50da40096d..f4805e15b29b016a2ddf78febad0971ee11d12c2 100644 (file)
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -150,7 +150,11 @@ 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_attach_filter(struct sock_fprog *fprog, struct sock *sk);

diff --git a/net/core/filter.c b/net/core/filter.c
index 9c88080e4049ceb83f1f27f5fecf94020a399263..62667722b5742ca3bb0ef86eee28c86f720b67ac 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -64,9 +64,10 @@ 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
@@ -75,7 +76,7 @@ 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;
@@ -88,14 +89,13 @@ 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

diff --git a/net/rose/rose_in.c b/net/rose/rose_in.c
index 7f7fcb46b4fa00371201dee0e83f17819db9c5e3..e5029c58e47259e23ee8d4410dd45b8b9be18431 100644 (file)
--- a/net/rose/rose_in.c
+++ b/net/rose/rose_in.c
@@ -165,7 +165,8 @@ static int rose_state3_machine(struct sock *sk, struct sk_buff *skb, int framety
                rose_frames_acked(sk, nr);
                if (ns == rose->vr) {
                        rose_start_idletimer(sk);
-                       if (sock_queue_rcv_skb(sk, skb) == 0) {
+                       if (sk_filter_trim_cap(sk, skb, ROSE_MIN_LEN) == 0 &&
+                           __sock_queue_rcv_skb(sk, skb) == 0) {
                                rose->vr = (rose->vr + 1) % ROSE_MODULUS;
                                queued = 1;
                        } else {