netdev - [PATCH net 3/3] net: strparser: partially revert "strparser: Call skb

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Date:   Wed, 10 Apr 2019 11:04:32 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     davem@...emloft.net
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org,
        alexei.starovoitov@...il.com, vakul.garg@....com,
        borisp@...lanox.com, Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Dirk van der Merwe <dirk.vandermerwe@...ronome.com>
Subject: [PATCH net 3/3] net: strparser: partially revert "strparser: Call skb_unclone conditionally"

This reverts the first part of commit 4e485d06bb8c ("strparser: Call
skb_unclone conditionally").  To build a message with multiple
fragments we need our own root of frag_list.  We can't simply
use the frag_list of orig_skb, because it will lead to linking
all orig_skbs together creating very long frag chains, and causing
stack overflow on kfree_skb() (which is called recursively on
the frag_lists).

BUG: stack guard page was hit at 00000000d40fad41 (stack is 0000000029dde9f4..000000008cce03d5)
kernel stack overflow (double-fault): 0000 [#1] PREEMPT SMP
RIP: 0010:free_one_page+0x2b/0x490

Call Trace:
  __free_pages_ok+0x143/0x2c0
  skb_release_data+0x8e/0x140
  ? skb_release_data+0xad/0x140
  kfree_skb+0x32/0xb0

  [...]

  skb_release_data+0xad/0x140
  ? skb_release_data+0xad/0x140
  kfree_skb+0x32/0xb0
  skb_release_data+0xad/0x140
  ? skb_release_data+0xad/0x140
  kfree_skb+0x32/0xb0
  skb_release_data+0xad/0x140
  ? skb_release_data+0xad/0x140
  kfree_skb+0x32/0xb0
  skb_release_data+0xad/0x140
  ? skb_release_data+0xad/0x140
  kfree_skb+0x32/0xb0
  skb_release_data+0xad/0x140
  __kfree_skb+0xe/0x20
  tcp_disconnect+0xd6/0x4d0
  tcp_close+0xf4/0x430
  ? tcp_check_oom+0xf0/0xf0
  tls_sk_proto_close+0xe4/0x1e0 [tls]
  inet_release+0x36/0x60
  __sock_release+0x37/0xa0
  sock_close+0x11/0x20
  __fput+0xa2/0x1d0
  task_work_run+0x89/0xb0
  exit_to_usermode_loop+0x9a/0xa0
  do_syscall_64+0xc0/0xf0
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Let's leave the second unclone conditional, as I'm not entirely
sure what is its purpose :)

Fixes: 4e485d06bb8c ("strparser: Call skb_unclone conditionally")
Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@...ronome.com>
---
 net/strparser/strparser.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c
index 860dcfb95ee4..fa6c977b4c41 100644
--- a/net/strparser/strparser.c
+++ b/net/strparser/strparser.c
@@ -140,13 +140,11 @@ static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
 			/* We are going to append to the frags_list of head.
 			 * Need to unshare the frag_list.
 			 */
-			if (skb_has_frag_list(head)) {
-				err = skb_unclone(head, GFP_ATOMIC);
-				if (err) {
-					STRP_STATS_INCR(strp->stats.mem_fail);
-					desc->error = err;
-					return 0;
-				}
+			err = skb_unclone(head, GFP_ATOMIC);
+			if (err) {
+				STRP_STATS_INCR(strp->stats.mem_fail);
+				desc->error = err;
+				return 0;
 			}

 			if (unlikely(skb_shinfo(head)->frag_list)) {
-- 
2.21.0