From e94e50bd88f7ed2f2d40c32c06efd61c36c33ec8 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Fri, 21 Dec 2018 19:03:13 +0100 Subject: [PATCH] net: fix possible user-after-free in skb_ext_add() On cow we can free the old extension: we must avoid dereferencing such extension after skb_ext_maybe_cow(). Since 'new' contents are always equal to 'old' after the copy, we can fix the above accessing the relevant data using 'new'. Fixes: df5042f4c5b9 ("sk_buff: add skb extension infrastructure") Signed-off-by: Paolo Abeni Acked-by: Florian Westphal Signed-off-by: David S. Miller --- net/core/skbuff.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index cb0bf4215745..e1d88762f659 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -5666,13 +5666,13 @@ void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id) if (!new) return NULL; - if (__skb_ext_exist(old, id)) { + if (__skb_ext_exist(new, id)) { if (old != new) skb->extensions = new; goto set_active; } - newoff = old->chunks; + newoff = new->chunks; } else { newoff = SKB_EXT_CHUNKSIZEOF(*new);