From: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Date: Fri, 30 Mar 2018 09:21:00 +0900
Subject: bpf: sockmap: initialize sg table entries properly
Patch-mainline: v4.17-rc1
Git-commit: 6ef6d84ceee2262a8c7a4247616c7eb71268b3f9
References: bsc#1109837

When CONFIG_DEBUG_SG is set, sg->sg_magic is initialized in
sg_init_table() and it is verified in sg api while navigating. We hit
BUG_ON when magic check is failed.

In functions sg_tcp_sendpage and sg_tcp_sendmsg, the struct containing
the scatterlist is already zeroed out. So to avoid extra memset, we
use sg_init_marker() to initialize sg_magic.

Fixed following things:
- In bpf_tcp_sendpage: initialize sg using sg_init_marker
- In bpf_tcp_sendmsg: Replace sg_init_table with sg_init_marker
- In bpf_tcp_push: Replace memset with sg_init_table where consumed
  sg entry needs to be re-initialized.

Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/sockmap.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -341,7 +341,7 @@ retry:
 			md->sg_start++;
 			if (md->sg_start == MAX_SKB_FRAGS)
 				md->sg_start = 0;
-			memset(sg, 0, sizeof(*sg));
+			sg_init_table(sg, 1);
 
 			if (md->sg_start == md->sg_end)
 				break;
@@ -843,7 +843,7 @@ static int bpf_tcp_sendmsg(struct sock *
 	}
 
 	sg = md.sg_data;
-	sg_init_table(sg, MAX_SKB_FRAGS);
+	sg_init_marker(sg, MAX_SKB_FRAGS);
 	rcu_read_unlock();
 
 	lock_sock(sk);
@@ -950,10 +950,14 @@ static int bpf_tcp_sendpage(struct sock
 
 	lock_sock(sk);
 
-	if (psock->cork_bytes)
+	if (psock->cork_bytes) {
 		m = psock->cork;
-	else
+		sg = &m->sg_data[m->sg_end];
+	} else {
 		m = &md;
+		sg = m->sg_data;
+		sg_init_marker(sg, MAX_SKB_FRAGS);
+	}
 
 	/* Catch case where ring is full and sendpage is stalled. */
 	if (unlikely(m->sg_end == m->sg_start &&
@@ -961,7 +965,6 @@ static int bpf_tcp_sendpage(struct sock
 		goto out_err;
 
 	psock->sg_size += size;
-	sg = &m->sg_data[m->sg_end];
 	sg_set_page(sg, page, size, offset);
 	get_page(page);
 	m->sg_copy[m->sg_end] = true;