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Wed, 4 Mar 2026 12:04:20 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id sDevCcQfqGkSdQAAD6G6ig (envelope-from ); Wed, 04 Mar 2026 12:04:20 +0000 From: Fernando Fernandez Mancera To: netdev@vger.kernel.org Cc: bridge@lists.linux.dev, roopa@cumulusnetworks.com, sdf@fomichev.me, petrm@nvidia.com, horms@kernel.org, idosch@nvidia.com, razor@blackwall.org, pabeni@redhat.com, kuba@kernel.org, edumazet@google.com, davem@davemloft.net, andrew+netdev@lunn.ch, Fernando Fernandez Mancera Subject: [PATCH 2/2 net v3] net: vxlan: fix nd_tbl NULL dereference when IPv6 is disabled Date: Wed, 4 Mar 2026 13:03:57 +0100 Message-ID: <20260304120357.9778-2-fmancera@suse.de> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260304120357.9778-1-fmancera@suse.de> References: <20260304120357.9778-1-fmancera@suse.de> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-1.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:email,imap1.dmz-prg2.suse.org:helo]; RCPT_COUNT_TWELVE(0.00)[14]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TAGGED_RCPT(0.00)[netdev]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_DN_SOME(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCVD_TLS_ALL(0.00)[] X-Spam-Flag: NO X-Spam-Score: -1.30 X-Spam-Level: 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 an IPv6 packet is injected into the interface, route_shortcircuit() is called and a NULL pointer dereference happens on neigh_lookup(). BUG: kernel NULL pointer dereference, address: 0000000000000380 Oops: Oops: 0000 [#1] SMP NOPTI [...] RIP: 0010:neigh_lookup+0x20/0x270 [...] Call Trace: vxlan_xmit+0x638/0x1ef0 [vxlan] dev_hard_start_xmit+0x9e/0x2e0 __dev_queue_xmit+0xbee/0x14e0 packet_sendmsg+0x116f/0x1930 __sys_sendto+0x1f5/0x200 __x64_sys_sendto+0x24/0x30 do_syscall_64+0x12f/0x1590 entry_SYSCALL_64_after_hwframe+0x76/0x7e Fix this by adding an early check on route_shortcircuit() when protocol is ETH_P_IPV6. Note that ipv6_mod_enabled() cannot be used here because VXLAN can be built-in even when IPv6 is built as a module. Fixes: e15a00aafa4b ("vxlan: add ipv6 route short circuit support") Signed-off-by: Fernando Fernandez Mancera --- v2: use ipv6_mod_enabled() instead of a NULL check v3: go back to nd_tbl NULL check as ipv6_mod_enabled() might not be available. Added a comment so it doesn't seem random. --- drivers/net/vxlan/vxlan_core.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c index 05558b6afecd..17c941aac32d 100644 --- a/drivers/net/vxlan/vxlan_core.c +++ b/drivers/net/vxlan/vxlan_core.c @@ -2130,6 +2130,11 @@ static bool route_shortcircuit(struct net_device *dev, struct sk_buff *skb) { struct ipv6hdr *pip6; + /* check if nd_tbl is not initiliazed due to + * ipv6.disable=1 set during boot + */ + if (!ipv6_stub->nd_tbl) + return false; if (!pskb_may_pull(skb, sizeof(struct ipv6hdr))) return false; pip6 = ipv6_hdr(skb); -- 2.53.0