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[net-next,v2,1/3] net: fix possible user-after-free in skb_ext_add()

Message ID d42c1c29b5201e140449c9a8d90f4bbc15574e89.1545413818.git.pabeni@redhat.com
State Accepted, archived
Delegated to: David Miller
Headers show
Series net: skb extension follow-ups | expand

Commit Message

Paolo Abeni Dec. 21, 2018, 6:03 p.m. UTC 
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 <pabeni@redhat.com>
Acked-by: Florian Westphal <fw@strlen.de>
---
 net/core/skbuff.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
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Patch

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);