[NET]: Make skb_seq_read unmap the last fragment

Having walked through the entire skbuff, skb_seq_read would leave the
last fragment mapped.  As a consequence, the unwary caller would leak
kmaps, and proceed with preempt_count off by one. The only (kind of
non-intuitive) workaround is to use skb_seq_read_abort.

This patch makes sure skb_seq_read always unmaps frag_data after
having cycled through the skb's paged part.

Signed-off-by: Olaf Kirch <olaf.kirch@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8d43ae6979e5..27cfe5fe4bb9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1706,6 +1706,11 @@ next_skb:
                 st->stepped_offset += frag->size;
         }
 
+        if (st->frag_data) {
+                kunmap_skb_frag(st->frag_data);
+                st->frag_data = NULL;
+        }
+
         if (st->cur_skb->next) {
                 st->cur_skb = st->cur_skb->next;
                 st->frag_idx = 0;