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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , =?UTF-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= , David Ahern , Jay Vosburgh , Andrew Lunn , Hangbin Liu Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260305-net-nd_tbl_fixes-v2-0-b7177db1a9f3@suse.com> <20260305-net-nd_tbl_fixes-v2-2-b7177db1a9f3@suse.com> Content-Language: en-US From: Fernando Fernandez Mancera In-Reply-To: <20260305-net-nd_tbl_fixes-v2-2-b7177db1a9f3@suse.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; FREEMAIL_TO(0.00)[suse.com,linux.dev,iogearbox.net,gmail.com,fomichev.me,kernel.org,google.com,davemloft.net,redhat.com,jvosburgh.net,lunn.ch]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCPT_COUNT_TWELVE(0.00)[26]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[netdev]; DKIM_TRACE(0.00)[suse.de:+]; R_RATELIMIT(0.00)[to_ip_from(RLjnappfs4fazzqxz8xagywz8p)]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:dkim,suse.de:email,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Score: -3.01 X-Spam-Level: X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: 69A243E77E On 3/5/26 9:37 PM, Ricardo B. Marlière wrote: > When booting with the 'ipv6.disable=1' parameter, the nd_tbl is never > initialized because inet6_init() exits before ndisc_init() is called which > initializes it. If bpf_redirect_neigh() is called with explicit AF_INET6 > nexthop parameters, __bpf_redirect_neigh_v6() can skip the IPv6 FIB lookup > and call bpf_out_neigh_v6() directly. bpf_out_neigh_v6() then calls > ip_neigh_gw6(), which uses ipv6_stub->nd_tbl. > > BUG: kernel NULL pointer dereference, address: 0000000000000248 > Oops: Oops: 0000 [#1] SMP NOPTI > RIP: 0010:skb_do_redirect+0x44f/0xf40 > Call Trace: > > ? srso_alias_return_thunk+0x5/0xfbef5 > ? __tcf_classify.constprop.0+0x83/0x160 > ? srso_alias_return_thunk+0x5/0xfbef5 > ? tcf_classify+0x2b/0x50 > ? srso_alias_return_thunk+0x5/0xfbef5 > ? tc_run+0xb8/0x120 > ? srso_alias_return_thunk+0x5/0xfbef5 > __dev_queue_xmit+0x6fa/0x1000 > ? srso_alias_return_thunk+0x5/0xfbef5 > packet_sendmsg+0x10da/0x1700 > ? srso_alias_return_thunk+0x5/0xfbef5 > __sys_sendto+0x1f3/0x220 > __x64_sys_sendto+0x24/0x30 > do_syscall_64+0x101/0xf80 > ? exc_page_fault+0x6e/0x170 > ? srso_alias_return_thunk+0x5/0xfbef5 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > Fix this by adding an early check in bpf_out_neigh_v6(). If > ipv6_stub->nd_tbl is NULL, drop the packet before neighbor lookup. > > Suggested-by: Fernando Fernandez Mancera > Fixes: ba452c9e996d ("bpf: Fix bpf_redirect_neigh helper api to support supplying nexthop") > Signed-off-by: Ricardo B. Marlière > --- > net/core/filter.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/net/core/filter.c b/net/core/filter.c > index ff02dbe4c94f..3344fa0789f0 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -2228,6 +2228,9 @@ static int bpf_out_neigh_v6(struct net *net, struct sk_buff *skb, > return -ENOMEM; > } > > + if (unlikely(!ipv6_mod_enabled())) > + goto out_drop; > + I don't think this is possible here if ipv6=m is set. Could you check that, please? A NULL check will be needed. See this similar situation: https://web.git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=168ff39e4758897d2eee4756977d036d52884c7e Bonding is fine as it enforces `depends on IPV6 || IPV6=n`. Thanks, Fernando. > rcu_read_lock(); > if (!nh) { > dst = skb_dst(skb); >