Toshiaki Makita <[email protected]> writes: > On 2020/07/06 21:29, Toke Høiland-Jørgensen wrote: >> Toshiaki pointed out that we now have two very similar functions to extract >> the L3 protocol number in the presence of VLAN tags. And Daniel pointed out >> that the unbounded parsing loop makes it possible for maliciously crafted >> packets to loop through potentially hundreds of tags. >> >> Fix both of these issues by consolidating the two parsing functions and >> limiting the VLAN tag parsing to an arbitrarily-chosen, but hopefully >> conservative, max depth of 32 tags. As part of this, switch over >> __vlan_get_protocol() to use skb_header_pointer() instead of >> pskb_may_pull(), to avoid the possible side effects of the latter and keep >> the skb pointer 'const' through all the parsing functions. >> >> Reported-by: Toshiaki Makita <[email protected]> >> Reported-by: Daniel Borkmann <[email protected]> >> Fixes: d7bf2ebebc2b ("sched: consistently handle layer3 header accesses in >> the presence of VLANs") >> Signed-off-by: Toke Høiland-Jørgensen <[email protected]> >> --- > ... >> @@ -623,13 +597,12 @@ static inline __be16 __vlan_get_protocol(struct >> sk_buff *skb, __be16 type, >> vlan_depth = ETH_HLEN; >> } >> do { >> - struct vlan_hdr *vh; >> + struct vlan_hdr vhdr, *vh; >> >> - if (unlikely(!pskb_may_pull(skb, >> - vlan_depth + VLAN_HLEN))) >> + vh = skb_header_pointer(skb, vlan_depth, sizeof(vhdr), >> &vhdr); > > Some drivers which use vlan_get_protocol to get IP protocol for checksum > offload discards > packets when it cannot get the protocol. > I guess for such users this function should try to get protocol even if it is > not in skb header? > I'm not sure such a case can happen, but since you care about this, you know > real cases where > vlan tag can be in skb frags?
skb_header_pointer() will still succeed in reading the data, it'll just do so by copying it into the buffer on the stack (vhdr) instead of moving the SKB data itself around... -Toke
