b975d3ee59
Years ago flow dissector gained ability to delegate flow dissection
to a bpf program, scoped per netns.
Unfortunately, skb_get_hash() only gets an sk_buff argument instead
of both net+skb. This means the flow dissector needs to obtain the
netns pointer from somewhere else.
The netns is derived from skb->dev, and if that is not available, from
skb->sk. If neither is set, we hit a (benign) WARN_ON_ONCE().
Trying both dev and sk covers most cases, but not all, as recently
reported by Christoph Paasch.
In case of nf-generated tcp reset, both sk and dev are NULL:
WARNING: .. net/core/flow_dissector.c:1104
skb_flow_dissect_flow_keys include/linux/skbuff.h:1536 [inline]
skb_get_hash include/linux/skbuff.h:1578 [inline]
nft_trace_init+0x7d/0x120 net/netfilter/nf_tables_trace.c:320
nft_do_chain+0xb26/0xb90 net/netfilter/nf_tables_core.c:268
nft_do_chain_ipv4+0x7a/0xa0 net/netfilter/nft_chain_filter.c:23
nf_hook_slow+0x57/0x160 net/netfilter/core.c:626
__ip_local_out+0x21d/0x260 net/ipv4/ip_output.c:118
ip_local_out+0x26/0x1e0 net/ipv4/ip_output.c:127
nf_send_reset+0x58c/0x700 net/ipv4/netfilter/nf_reject_ipv4.c:308
nft_reject_ipv4_eval+0x53/0x90 net/ipv4/netfilter/nft_reject_ipv4.c:30
[..]
syzkaller did something like this:
table inet filter {
chain input {
type filter hook input priority filter; policy accept;
meta nftrace set 1
tcp dport 42 reject with tcp reset
}
chain output {
type filter hook output priority filter; policy accept;
# empty chain is enough
}
}
... then sends a tcp packet to port 42.
Initial attempt to simply set skb->dev from nf_reject_ipv4 doesn't cover
all cases: skbs generated via ipv4 igmp_send_report trigger similar splat.
Moreover, Pablo Neira found that nft_hash.c uses __skb_get_hash_symmetric()
which would trigger same warn splat for such skbs.
Lets allow callers to pass the current netns explicitly.
The nf_trace infrastructure is adjusted to use the new helper.
__skb_get_hash_symmetric is handled in the next patch.
Reported-by: Christoph Paasch <cpaasch@apple.com>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/494
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240608221057.16070-2-fw@strlen.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.