[PATCH v1 net] udplite: Fix null-ptr-deref in __udp_enqueue_schedule_skb().

[PATCH v1 net] udplite: Fix null-ptr-deref in __udp_enqueue_schedule_skb().

[Kuniyuki Iwashima]

syzbot reported null-ptr-deref of udp_sk(sk)->udp_prod_queue. [0]

Since the cited commit, udp_lib_init_sock() can fail, as can
udp_init_sock() and udpv6_init_sock().

Let's handle the error in udplite_sk_init() and udplitev6_sk_init().

[0]:
BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:82 [inline]
BUG: KASAN: null-ptr-deref in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
BUG: KASAN: null-ptr-deref in __udp_enqueue_schedule_skb+0x151/0x1480 net/ipv4/udp.c:1719
Read of size 4 at addr 0000000000000008 by task syz.2.18/2944

CPU: 1 UID: 0 PID: 2944 Comm: syz.2.18 Not tainted syzkaller #0 PREEMPTLAZY
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 kasan_report+0xa2/0xe0 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read include/linux/instrumented.h:82 [inline]
 atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
 __udp_enqueue_schedule_skb+0x151/0x1480 net/ipv4/udp.c:1719
 __udpv6_queue_rcv_skb net/ipv6/udp.c:795 [inline]
 udpv6_queue_rcv_one_skb+0xa2e/0x1ad0 net/ipv6/udp.c:906
 udp6_unicast_rcv_skb+0x227/0x380 net/ipv6/udp.c:1064
 ip6_protocol_deliver_rcu+0xe17/0x1540 net/ipv6/ip6_input.c:438
 ip6_input_finish+0x191/0x350 net/ipv6/ip6_input.c:489
 NF_HOOK+0x354/0x3f0 include/linux/netfilter.h:318
 ip6_input+0x16c/0x2b0 net/ipv6/ip6_input.c:500
 NF_HOOK+0x354/0x3f0 include/linux/netfilter.h:318
 __netif_receive_skb_one_core net/core/dev.c:6149 [inline]
 __netif_receive_skb+0xd3/0x370 net/core/dev.c:6262
 process_backlog+0x4d6/0x1160 net/core/dev.c:6614
 __napi_poll+0xae/0x320 net/core/dev.c:7678
 napi_poll net/core/dev.c:7741 [inline]
 net_rx_action+0x60d/0xdc0 net/core/dev.c:7893
 handle_softirqs+0x209/0x8d0 kernel/softirq.c:622
 do_softirq+0x52/0x90 kernel/softirq.c:523
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0xe7/0x120 kernel/softirq.c:450
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:924 [inline]
 __dev_queue_xmit+0x109c/0x2dc0 net/core/dev.c:4856
 __ip6_finish_output net/ipv6/ip6_output.c:-1 [inline]
 ip6_finish_output+0x158/0x4e0 net/ipv6/ip6_output.c:219
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip6_output+0x342/0x580 net/ipv6/ip6_output.c:246
 ip6_send_skb+0x1d7/0x3c0 net/ipv6/ip6_output.c:1984
 udp_v6_send_skb+0x9a5/0x1770 net/ipv6/udp.c:1442
 udp_v6_push_pending_frames+0xa2/0x140 net/ipv6/udp.c:1469
 udpv6_sendmsg+0xfe0/0x2830 net/ipv6/udp.c:1759
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0xe5/0x270 net/socket.c:742
 __sys_sendto+0x3eb/0x580 net/socket.c:2206
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2209
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0xf20 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f67b4d9c629
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f67b5c98028 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007f67b5015fa0 RCX: 00007f67b4d9c629
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f67b4e32b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000040000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f67b5016038 R14: 00007f67b5015fa0 R15: 00007ffe3cb66dd8
 </TASK>

Fixes: b650bf0977d3 ("udp: remove busylock and add per NUMA queues")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
I'll remove UDP-Lite entirely once net-next opens next week.
---
 net/ipv4/udplite.c | 3 +--
 net/ipv6/udplite.c | 3 +--
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/udplite.c b/net/ipv4/udplite.c
index d3e621a11a1a..826e9e79eb19 100644
--- a/net/ipv4/udplite.c
+++ b/net/ipv4/udplite.c
@@ -20,10 +20,9 @@ EXPORT_SYMBOL(udplite_table);
 /* Designate sk as UDP-Lite socket */
 static int udplite_sk_init(struct sock *sk)
 {
-	udp_init_sock(sk);
 	pr_warn_once("UDP-Lite is deprecated and scheduled to be removed in 2025, "
 		     "please contact the netdev mailing list\n");
-	return 0;
+	return udp_init_sock(sk);
 }
 
 static int udplite_rcv(struct sk_buff *skb)
diff --git a/net/ipv6/udplite.c b/net/ipv6/udplite.c
index 2cec542437f7..e867721cda4d 100644
--- a/net/ipv6/udplite.c
+++ b/net/ipv6/udplite.c
@@ -16,10 +16,9 @@
 
 static int udplitev6_sk_init(struct sock *sk)
 {
-	udpv6_init_sock(sk);
 	pr_warn_once("UDP-Lite is deprecated and scheduled to be removed in 2025, "
 		     "please contact the netdev mailing list\n");
-	return 0;
+	return udpv6_init_sock(sk);
 }
 
 static int udplitev6_rcv(struct sk_buff *skb)
-- 
2.53.0.345.g96ddfc5eaa-goog

Re: [PATCH v1 net] udplite: Fix null-ptr-deref in __udp_enqueue_schedule_skb().

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 19 Feb 2026 17:31:31 +0000 you wrote:
> syzbot reported null-ptr-deref of udp_sk(sk)->udp_prod_queue. [0]
> 
> Since the cited commit, udp_lib_init_sock() can fail, as can
> udp_init_sock() and udpv6_init_sock().
> 
> Let's handle the error in udplite_sk_init() and udplitev6_sk_init().
> 
> [...]

Here is the summary with links:
  - [v1,net] udplite: Fix null-ptr-deref in __udp_enqueue_schedule_skb().
    https://git.kernel.org/netdev/net/c/470c7ca2b4c3

You are awesome, thank you!
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