From: Fred Li <dracodingfly@xxxxxxxxx>
The crashed kernel version is 5.16.20, and I have not test this patch
because I dont find a way to reproduce it, and the mailine may be
has the same problem.
When using bpf based NAT, hits a kernel BUG_ON at function skb_segment(),
BUG_ON(skb_headlen(list_skb) > len). The bpf calls the bpf_skb_adjust_room
to decrease the gso_size, and then call bpf_redirect send packet out.
call stack:
...
[exception RIP: skb_segment+3016]
RIP: ffffffffb97df2a8 RSP: ffffa3f2cce08728 RFLAGS: 00010293
RAX: 000000000000007d RBX: 00000000fffff7b3 RCX: 0000000000000011
RDX: 0000000000000000 RSI: ffff895ea32c76c0 RDI: 00000000000008c1
RBP: ffffa3f2cce087f8 R8: 000000000000088f R9: 0000000000000011
R10: 000000000000090c R11: ffff895e47e68000 R12: ffff895eb2022f00
R13: 000000000000004b R14: ffff895ecdaf2000 R15: ffff895eb2023f00
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#9 [ffffa3f2cce08720] skb_segment at ffffffffb97ded63
#10 [ffffa3f2cce08800] tcp_gso_segment at ffffffffb98d0320
#11 [ffffa3f2cce08860] tcp4_gso_segment at ffffffffb98d07a3
#12 [ffffa3f2cce08880] inet_gso_segment at ffffffffb98e6de0
#13 [ffffa3f2cce088e0] skb_mac_gso_segment at ffffffffb97f3741
#14 [ffffa3f2cce08918] skb_udp_tunnel_segment at ffffffffb98daa59
#15 [ffffa3f2cce08980] udp4_ufo_fragment at ffffffffb98db471
#16 [ffffa3f2cce089b0] inet_gso_segment at ffffffffb98e6de0
#17 [ffffa3f2cce08a10] skb_mac_gso_segment at ffffffffb97f3741
#18 [ffffa3f2cce08a48] __skb_gso_segment at ffffffffb97f388e
#19 [ffffa3f2cce08a78] validate_xmit_skb at ffffffffb97f3d6e
#20 [ffffa3f2cce08ab8] __dev_queue_xmit at ffffffffb97f4614
#21 [ffffa3f2cce08b50] dev_queue_xmit at ffffffffb97f5030
#22 [ffffa3f2cce08b60] __bpf_redirect at ffffffffb98199a8
#23 [ffffa3f2cce08b88] skb_do_redirect at ffffffffb98205cd
...
The skb has the following properties:
doffset = 66
list_skb = skb_shinfo(skb)->frag_list
list_skb->head_frag = true
skb->len = 2441 && skb->data_len = 2250
skb_shinfo(skb)->nr_frags = 17
skb_shinfo(skb)->gso_size = 75
skb_shinfo(skb)->frags[0...16].bv_len = 125
list_skb->len = 125
list_skb->data_len = 0
3962 struct sk_buff *skb_segment(struct sk_buff *head_skb,
3963 netdev_features_t features)
3964 {
3965 struct sk_buff *segs = NULL;
3966 struct sk_buff *tail = NULL;
...
4181 while (pos < offset + len) {
4182 if (i >= nfrags) {
4183 i = 0;
4184 nfrags = skb_shinfo(list_skb)->nr_frags;
4185 frag = skb_shinfo(list_skb)->frags;
4186 frag_skb = list_skb;
After segment the head_skb's last frag, the (pos == offset+len), so break the
while at line 4181, run into this BUG_ON(), not segment the head_frag frag_list
skb.
Since commit 13acc94eff122(net: permit skb_segment on head_frag frag_list skb),
it is allowed to segment the head_frag frag_list skb.
In commit 3dcbdb134f32 (net: gso: Fix skb_segment splat when splitting gso_size
mangled skb having linear-headed frag_list), it is cleared the NETIF_F_SG if it
has non head_frag skb. It is not cleared the NETIF_F_SG only with one head_frag
frag_list skb.
Signed-off-by: Fred Li <dracodingfly@xxxxxxxxx>
---
net/core/skbuff.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 001152c..d805a47 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4070,7 +4070,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
hsize = skb_headlen(head_skb) - offset;
- if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) &&
+ if (hsize <= 0 && i >= nfrags && !list_skb->head_frag && skb_headlen(list_skb) &&
(skb_headlen(list_skb) == len || sg)) {
BUG_ON(skb_headlen(list_skb) > len);
--
1.8.3.1
