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Sat, 28 Feb 2026 09:46:50 -0800 (PST) From: =?utf-8?q?Ricardo_B=2E_Marli=C3=A8re?= Date: Sat, 28 Feb 2026 14:46:26 -0300 Subject: [PATCH net 1/3] bpf: bpf_out_neigh_v4: Fix nd_tbl NULL dereference when IPv6 is disabled Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Message-Id: <20260228-net-nd_tbl_fixes-v1-1-2b2a274df9bb@suse.com> References: <20260228-net-nd_tbl_fixes-v1-0-2b2a274df9bb@suse.com> In-Reply-To: <20260228-net-nd_tbl_fixes-v1-0-2b2a274df9bb@suse.com> To: Martin KaFai Lau , Daniel Borkmann , John Fastabend , Stanislav Fomichev , Alexei Starovoitov , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , "David S. 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: Fernando Fernandez Mancera , bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, =?utf-8?q?Ricardo_B=2E_Marli=C3=A8re?= X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openssh-sha256; t=1772300803; l=2182; i=rbm@suse.com; h=from:subject:message-id; bh=ucFGNhQbyvRgliJm2iclmlbV7LXFrBb9Ujgx98X8vXQ=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgguRCc5X8/UX9M40lkMnr//aFGOhce x5ezt8MFNUFlqYAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QLqZmcEzlqILSWD7UP8bPCY/O1xURrrkYnEZviyYV9TEw84KCTDDT97+pGEpf5s2Sx5NOTFb0HA dNu1zqk+zRwU= X-Developer-Key: i=rbm@suse.com; a=openssh; fpr=SHA256:pzhe0fJpYLz+3cZ33FFPhIfaUElk9CXPFFXmalIH+1g 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 from tc with an explicit nexthop of nh_family == AF_INET6, bpf_out_neigh_v4() takes the AF_INET6 branch and calls ip_neigh_gw6(), which relies on ipv6_stub->nd_tbl. BUG: kernel NULL pointer dereference, address: 0000000000000248 Oops: Oops: 0000 [#1] SMP NOPTI RIP: 0010:skb_do_redirect+0xb93/0xf00 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 ? srso_alias_return_thunk+0x5/0xfbef5 ? alloc_skb_with_frags+0x58/0x200 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 the AF_INET6 branch of bpf_out_neigh_v4(). If ipv6_stub->nd_tbl is NULL, unlock RCU and drop the packet. 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 | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/core/filter.c b/net/core/filter.c index 0d5d5a17acb2..9ab2fae3a0d9 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2335,6 +2335,10 @@ static int bpf_out_neigh_v4(struct net *net, struct sk_buff *skb, neigh = ip_neigh_for_gw(rt, skb, &is_v6gw); } else if (nh->nh_family == AF_INET6) { + if (!ipv6_stub->nd_tbl) { + rcu_read_unlock(); + goto out_drop; + } neigh = ip_neigh_gw6(dev, &nh->ipv6_nh); is_v6gw = true; } else if (nh->nh_family == AF_INET) { -- 2.53.0