[PATCH AUTOSEL 4.19 78/81] net: strparser: partially revert "strparser: Call skb_unclone conditionally"

Sasha Levin
2019-05-07T05:38:22Z

From: Jakub Kicinski <jakub.kicinski@netronome.com>

[ Upstream commit 4a9c2e3746e6151fd5d077259d79ce9ca86d47d7 ]

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@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.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 da1a676860ca..0f4e42792878 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)) {
--
2.20.1