Re: [PATCH IPV6 1/1] ipv6: allocate enough headroom in ip6_finish_output2()

On 7/7/21 8:30 PM, Jakub Kicinski wrote:

On Wed, 7 Jul 2021 19:41:44 +0200 Eric Dumazet wrote:

quoted

On 7/7/21 6:42 PM, Jakub Kicinski wrote:

quoted

On Wed, 7 Jul 2021 08:45:13 -0600 David Ahern wrote:  

quoted

why not use hh_len here?  

Is there a reason for the new skb? Why not pskb_expand_head()?  

pskb_expand_head() might crash, if skb is shared.

We possibly can add a helper, factorizing all this,
and eventually use pskb_expand_head() if safe.

Is there a strategically placed skb_share_check() somewhere further
down? Otherwise there seems to be a lot of questionable skb_cow*()
calls, also __skb_linearize() and skb_pad() are risky, no?
Or is it that shared skbs are uncommon and syzbot doesn't hit them?

Some of us try hard to remove skb_get() occurrences,
but they tend to re-appear fast :/

Refs: commit a516993f0ac1694673412eb2d16a091eafa77d2a
("net: fix wrong skb_get() usage / crash in IGMP/MLD parsing code")