ip6mr: clear skb->cb[] in reg_vif_xmit()

reg_vif_xmit() hands the skb to ip6mr_cache_report() as an
MRT6MSG_WHOLEPKT report. skb_realloc_headroom() copies skb->cb[]
into the report, which is queued to the mroute socket, where
rawv6_recvmsg() reads it as IP6CB.

By the time the pim6reg device transmits the packet, skb->cb[] is
not IP6CB anymore: qdisc_pkt_len_init() overwrites iif and ra,
and any qdisc installed on the device (fq, fq_codel, pie, cake...)
or a tc BPF program writing skb->cb[] fills the area holding
dst0, srcrt, dst1, lastopt and flags.

Since commit dd433671fef3 ("ipv6: validate extension header length
before copying to cmsg") these stale offsets can no longer cause
out-of-bounds reads, but the mroute socket can still receive bogus
IPV6_PKTINFO ifindex and extension header ancillary data.

Clear IP6CB before building the report. The skb is freed right
after, so nothing else depends on its control block.

Fixes: 14fb64e1f449 ("[IPV6] MROUTE: Support PIM-SM (SSM).")
Signed-off-by: Eric Dumazet <edumazet@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions