[PATCH net, v3] net: nsh: Use correct mac_offset to unwind gso skb in nsh_gso_segment()
From: Dong Chenchen
Date: Tue May 09 2023 - 09:56:02 EST
As the call trace shows, skb_panic was caused by wrong skb->mac_header
in nsh_gso_segment():
invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 3 PID: 2737 Comm: syz Not tainted 6.3.0-next-20230505 #1
RIP: 0010:skb_panic+0xda/0xe0
call Trace:
skb_push+0x91/0xa0
nsh_gso_segment+0x4f3/0x570
skb_mac_gso_segment+0x19e/0x270
__skb_gso_segment+0x1e8/0x3c0
validate_xmit_skb+0x452/0x890
validate_xmit_skb_list+0x99/0xd0
sch_direct_xmit+0x294/0x7c0
__dev_queue_xmit+0x16f0/0x1d70
packet_xmit+0x185/0x210
packet_snd+0xc15/0x1170
packet_sendmsg+0x7b/0xa0
sock_sendmsg+0x14f/0x160
The root cause is:
nsh_gso_segment() use skb->network_header - nhoff to reset mac_header
in skb_gso_error_unwind() if inner-layer protocol gso fails.
However, skb->network_header may be reset by inner-layer protocol
gso function e.g. mpls_gso_segment. skb->mac_header reset by the
inaccurate network_header will be larger than skb headroom.
nsh_gso_segment
nhoff = skb->network_header - skb->mac_header;
__skb_pull(skb,nsh_len)
skb_mac_gso_segment
mpls_gso_segment
skb_reset_network_header(skb);//skb->network_header+=nsh_len
return -EINVAL;
skb_gso_error_unwind
skb_push(skb, nsh_len);
skb->mac_header = skb->network_header - nhoff;
// skb->mac_header > skb->headroom, cause skb_push panic
Use correct mac_offset to restore mac_header to fix it.
Fixes: c411ed854584 ("nsh: add GSO support")
Signed-off-by: Dong Chenchen <dongchenchen2@xxxxxxxxxx>
---
v2:
- Use skb->mac_header not skb->network_header-nhoff for mac_offset.
v3:
- 'net' is noted in the subject.
- arrange local variable following reverse xmas tree order
---
net/nsh/nsh.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/nsh/nsh.c b/net/nsh/nsh.c
index e9ca007718b7..793e0bd94558 100644
--- a/net/nsh/nsh.c
+++ b/net/nsh/nsh.c
@@ -77,6 +77,7 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
netdev_features_t features)
{
struct sk_buff *segs = ERR_PTR(-EINVAL);
+ u16 mac_offset = skb->mac_header;
unsigned int nsh_len, mac_len;
__be16 proto;
int nhoff;
@@ -108,8 +109,7 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
segs = skb_mac_gso_segment(skb, features);
if (IS_ERR_OR_NULL(segs)) {
skb_gso_error_unwind(skb, htons(ETH_P_NSH), nsh_len,
- skb->network_header - nhoff,
- mac_len);
+ mac_offset, mac_len);
goto out;
}
--
2.25.1