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 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 96509e579d21a9544c44adc48c34f04ae368324f..bdc6f86e78978226bf0b45944fc0539b50e98708 100644 (file)
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -346,7 +346,11 @@ static inline unsigned int sk_filter_size(unsigned int proglen)
 #define sk_filter_proglen(fprog)                       \
                (fprog->len * sizeof(fprog->filter[0]))
 
-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);
+}
 
 void sk_filter_select_runtime(struct sk_filter *fp);
 void sk_filter_free(struct sk_filter *fp);

diff --git a/net/core/filter.c b/net/core/filter.c
index b275c5559dc0efef49eaeb8610ab28ed78509133..fd6da397ea8c366e273acc895bc3bba3776cc4f6 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -94,9 +94,10 @@ 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
@@ -105,7 +106,7 @@ 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;
@@ -126,14 +127,13 @@ 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);
 
 /* Base function for offset calculation. Needs to go into .text section,
  * therefore keeping it non-static as well; will also be used by JITs

diff --git a/net/rose/rose_in.c b/net/rose/rose_in.c
index 79c4abcfa6b4ee86fbd92358f5585f88b74319f5..0a6394754e81db5469906b92f4b40046444bdb42 100644 (file)
--- a/net/rose/rose_in.c
+++ b/net/rose/rose_in.c
@@ -164,7 +164,8 @@ 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 {