[PATCH] tcp: detect use sendpage for slab-based objects

[Vasily Averin]

There was few incidents when XFS over network block device generates
IO requests with slab-based metadata. If these requests are processed
via sendpage path tcp_sendpage() calls skb_can_coalesce() and merges
neighbour slab objects into one skb fragment.

If receiving side is located on the same host tcp_recvmsg() can trigger
following BUG_ON
usercopy: kernel memory exposure attempt detected
                from XXXXXX (kmalloc-512) (1024 bytes)

This patch helps to detect the reason of similar incidents on sending side.

Signed-off-by: Vasily Averin <v...@virtuozzo.com>
---
 net/ipv4/tcp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 2079145a3b7c..cf9572f4fc0f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -996,6 +996,7 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page 
*page, int offset,
                        goto wait_for_memory;
 
                if (can_coalesce) {
+                       WARN_ON_ONCE(PageSlab(page));
                        skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
                } else {
                        get_page(page);
-- 
2.17.1