[PATCH net-next] flow_dissector: fix ipv6 dst, hop-by-hop and routing ext hdrs

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

__skb_header_pointer() returns a pointer that must be checked.

Fixes infinite loop reported by Alexei, and add __must_check to
catch these errors earlier.

Fixes: 6a74fcf426f5 ("flow_dissector: add support for dst, hop-by-hop and 
routing ext hdrs")
Reported-by: Alexei Starovoitov <alexei.starovoi...@gmail.com>
Tested-by: Alexei Starovoitov <alexei.starovoi...@gmail.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 include/linux/skbuff.h    |    9 +++++----
 net/core/flow_dissector.c |    6 ++++--
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 
cc612fc0a8943ec853b92e6b3516b0e5582299e2..a7acc92aa6685d7006077510697e3d9481b02588
 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2743,8 +2743,9 @@ __wsum __skb_checksum(const struct sk_buff *skb, int 
offset, int len,
 __wsum skb_checksum(const struct sk_buff *skb, int offset, int len,
                    __wsum csum);
 
-static inline void *__skb_header_pointer(const struct sk_buff *skb, int offset,
-                                        int len, void *data, int hlen, void 
*buffer)
+static inline void * __must_check
+__skb_header_pointer(const struct sk_buff *skb, int offset,
+                    int len, void *data, int hlen, void *buffer)
 {
        if (hlen - offset >= len)
                return data + offset;
@@ -2756,8 +2757,8 @@ static inline void *__skb_header_pointer(const struct 
sk_buff *skb, int offset,
        return buffer;
 }
 
-static inline void *skb_header_pointer(const struct sk_buff *skb, int offset,
-                                      int len, void *buffer)
+static inline void * __must_check
+skb_header_pointer(const struct sk_buff *skb, int offset, int len, void 
*buffer)
 {
        return __skb_header_pointer(skb, offset, len, skb->data,
                                    skb_headlen(skb), buffer);
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 
22e4dffa0c8b3b9a20a7324eae1627313e14ce30..476e5dda59e19822dba98a931369ff2666c59c0d
 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -394,9 +394,11 @@ ip_proto_again:
 
                opthdr = __skb_header_pointer(skb, nhoff, sizeof(_opthdr),
                                              data, hlen, &_opthdr);
+               if (!opthdr)
+                       return false;
 
-               ip_proto = _opthdr[0];
-               nhoff += (_opthdr[1] + 1) << 3;
+               ip_proto = opthdr[0];
+               nhoff += (opthdr[1] + 1) << 3;
 
                goto ip_proto_again;
        }


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