llc: Fix length check in llc_fixup_skb().

Fixes bugzilla #32872

The LLC stack pretends to support non-linear skbs but there is a
direct use of skb_tail_pointer() in llc_fixup_skb().

Use pskb_may_pull() to see if data_size bytes remain and can be
accessed linearly in the packet, instead of direct pointer checks.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 2 deletions

diff --git a/net/llc/llc_input.c b/net/llc/llc_input.c
index 058f1e9a9128..903242111317 100644
--- a/net/llc/llc_input.c
+++ b/net/llc/llc_input.c
@@ -121,8 +121,7 @@ static inline int llc_fixup_skb(struct sk_buff *skb)
                 s32 data_size = ntohs(pdulen) - llc_len;
 
                 if (data_size < 0 ||
-                    ((skb_tail_pointer(skb) -
-                      (u8 *)pdu) - llc_len) < data_size)
+                    !pskb_may_pull(skb, data_size))
                         return 0;
                 if (unlikely(pskb_trim_rcsum(skb, data_size)))
                         return 0;