Messages in this thread | | | From | Eric Dumazet <> | Date | Wed, 20 Mar 2024 14:43:22 +0100 | Subject | Re: [PATCH] flow_dissector: prevent NULL pointer dereference in __skb_flow_dissect |
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On Wed, Mar 20, 2024 at 2:38 PM Jiri Pirko <jiri@resnulli.us> wrote: > > Wed, Mar 20, 2024 at 01:56:35PM CET, abelova@astralinux.ru wrote: > >skb is an optional parameter, so it may be NULL. > >Add check defore dereference in eth_hdr. > > > >Found by Linux Verification Center (linuxtesting.org) with SVACE. > > Either drop this line which provides no value, or attach a link to the > actual report. > > > > > >Fixes: 67a900cc0436 ("flow_dissector: introduce support for Ethernet addresses") > > This looks incorrect. I believe that this is the offending commit: > commit 690e36e726d00d2528bc569809048adf61550d80 > Author: David S. Miller <davem@davemloft.net> > Date: Sat Aug 23 12:13:41 2014 -0700 > > net: Allow raw buffers to be passed into the flow dissector. > > > > >Signed-off-by: Anastasia Belova <abelova@astralinux.ru> > >--- > > net/core/flow_dissector.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > >diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c > >index 272f09251343..05db3a8aa771 100644 > >--- a/net/core/flow_dissector.c > >+++ b/net/core/flow_dissector.c > >@@ -1137,7 +1137,7 @@ bool __skb_flow_dissect(const struct net *net, > > rcu_read_unlock(); > > } > > > >- if (dissector_uses_key(flow_dissector, > >+ if (skb && dissector_uses_key(flow_dissector, > > FLOW_DISSECTOR_KEY_ETH_ADDRS)) { > > struct ethhdr *eth = eth_hdr(skb); > > struct flow_dissector_key_eth_addrs *key_eth_addrs; > > Looks like FLOW_DISSECT_RET_OUT_BAD should be returned in case the > FLOW_DISSECTOR_KEY_ETH_ADDRS are selected and there is no skb, no? >
It would be nice knowing in which context we could have a NULL skb and FLOW_DISSECTOR_KEY_ETH_ADDRS at the same time.
It seems this fix is based on some kind of static analysis, but no real bug.
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