Re: [PATCH] net: fix wrong skb_get() usage / crash in IGMP/MLD parsing code

On Thu, Aug 13, 2015 at 05:54:07AM +0200, Linus Lüssing wrote:

The recent refactoring of the IGMP and MLD parsing code into
ipv6_mc_check_mld() / ip_mc_check_igmp() introduced a potential crash /
BUG() invocation for bridges:

I wrongly assumed that skb_get() could be used as a simple reference
counter for an skb which is not the case. skb_get() bears additional
semantics, a user count. This leads to a BUG() invocation in
pskb_expand_head() / kernel panic if pskb_may_pull() is called on an skb
with a user count greater than one - unfortunately the refactoring did
just that.

Fixing this by removing the skb_get() call and changing the API: The
caller of ipv6_mc_check_mld() / ip_mc_check_igmp() now needs to
additionally check whether the returned skb_trimmed is a clone.

Fixes: 9afd85c9e455 ("net: Export IGMP/MLD message validation code")
Reported-by: Brenden Blanco <redacted>
Signed-off-by: Linus Lüssing <redacted>

I think the fix actually made the code easier to read.
Thank you. Looks good to me.
Acked-by: Alexei Starovoitov <redacted>