• Florian Westphal's avatar
    bridge: fix potential use-after-free when hook returns QUEUE or STOLEN verdict · 8626c56c
    Florian Westphal authored
    Zefir Kurtisi reported kernel panic with an openwrt specific patch.
    However, it turns out that mainline has a similar bug waiting to happen.
    
    Once NF_HOOK() returns the skb is in undefined state and must not be
    used.   Moreover, the okfn must consume the skb to support async
    processing (NF_QUEUE).
    
    Current okfn in this spot doesn't consume it and caller assumes that
    NF_HOOK return value tells us if skb was freed or not, but thats wrong.
    
    It "works" because no in-tree user registers a NFPROTO_BRIDGE hook at
    LOCAL_IN that returns STOLEN or NF_QUEUE verdicts.
    
    Once we add NF_QUEUE support for nftables bridge this will break --
    NF_QUEUE holds the skb for async processing, caller will erronoulsy
    return RX_HANDLER_PASS and on reinject netfilter will access free'd skb.
    
    Fix this by pushing skb up the stack in the okfn instead.
    
    NB: It also seems dubious to use LOCAL_IN while bypassing PRE_ROUTING
    completely in this case but this is how its been forever so it seems
    preferable to not change this.
    
    Cc: Felix Fietkau <nbd@openwrt.org>
    Cc: Zefir Kurtisi <zefir.kurtisi@neratec.com>
    Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
    Tested-by: default avatarZefir Kurtisi <zefir.kurtisi@neratec.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    8626c56c
br_input.c 7.79 KB