[PATCH v3 nf] netfilter: seqadj: Fix one possible panic in seqadj when mem is exhausted

From: Gao Feng <redacted>

When memory is exhausted, nfct_seqadj_ext_add may fail to add the seqadj
extension. But the function nf_ct_seqadj_init doesn't check if get valid
seqadj pointer by the nfct_seqadj, while other functions perform the
sanity check.

So the system would be panic when nfct_seqadj_ext_add failed.

Signed-off-by: Gao Feng <redacted>
---
 v3: Remove the warning log when seqadj is null;
 v2: Remove the unnessary seqadj check in nf_ct_seq_adjust
 v1: Initial patch

 net/netfilter/nf_conntrack_seqadj.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_seqadj.c b/net/netfilter/nf_conntrack_seqadj.c
index dff0f0c..7f8d814 100644
--- a/net/netfilter/nf_conntrack_seqadj.c
+++ b/net/netfilter/nf_conntrack_seqadj.c

@@ -16,9 +16,12 @@ int nf_ct_seqadj_init(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 	if (off == 0)
 		return 0;
 
+	seqadj = nfct_seqadj(ct);
+	if (unlikely(!seqadj))
+		return 0;