sockmap: Fix use-after-free in udp_bpf_recvmsg()

syzbot reported use-after-free of struct sk_msg in sk_msg_recvmsg(). [0]

sk_msg_recvmsg() peeks sk_msg from psock->ingress_msg under a lock,
but its processing is lockless.

Thus, sk_msg_recvmsg() must be serialised by callers, otherwise
multiple threads could touch the same sk_msg.

For example, TCP uses lock_sock(), and AF_UNIX uses unix_sk(sk)->iolock.

Initially, udp_bpf_recvmsg() had used lock_sock(), but the cited
commit removed it.

Let's serialise sk_msg_recvmsg() with lock_sock() in udp_bpf_recvmsg().

Note that holding spin_lock_bh(&sk->sk_receive_queue.lock) is not
an option due to copy_page_to_iter() in sk_msg_recvmsg().

[0]:
BUG: KASAN: slab-use-after-free in sk_msg_recvmsg+0xb54/0xc30 net/core/skmsg.c:428
Read of size 4 at addr ffff88814cdcf000 by task syz.0.24/6020

CPU: 1 UID: 0 PID: 6020 Comm: syz.0.24 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 sk_msg_recvmsg+0xb54/0xc30 net/core/skmsg.c:428
 udp_bpf_recvmsg+0x4bd/0xe00 net/ipv4/udp_bpf.c:84
 inet_recvmsg+0x260/0x270 net/ipv4/af_inet.c:891
 sock_recvmsg_nosec net/socket.c:1078 [inline]
 sock_recvmsg+0x1a8/0x270 net/socket.c:1100
 ____sys_recvmsg+0x1e6/0x4a0 net/socket.c:2812
 ___sys_recvmsg+0x215/0x590 net/socket.c:2854
 do_recvmmsg+0x334/0x800 net/socket.c:2949
 __sys_recvmmsg net/socket.c:3023 [inline]
 __do_sys_recvmmsg net/socket.c:3046 [inline]
 __se_sys_recvmmsg net/socket.c:3039 [inline]
 __x64_sys_recvmmsg+0x198/0x250 net/socket.c:3039
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb319f9aeb9
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:00007fb31ad97028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007fb31a216090 RCX: 00007fb319f9aeb9
RDX: 0000000000000001 RSI: 0000200000000400 RDI: 0000000000000004
RBP: 00007fb31a008c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000040000021 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb31a216128 R14: 00007fb31a216090 R15: 00007ffe21dd0a98
 </TASK>

Allocated by task 6019:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x3d1/0x6e0 mm/slub.c:5780
 kmalloc_noprof include/linux/slab.h:957 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 alloc_sk_msg net/core/skmsg.c:510 [inline]
 sk_psock_skb_ingress_self+0x60/0x350 net/core/skmsg.c:612
 sk_psock_verdict_apply net/core/skmsg.c:1038 [inline]
 sk_psock_verdict_recv+0x7d9/0x8d0 net/core/skmsg.c:1236
 udp_read_skb+0x73e/0x7e0 net/ipv4/udp.c:2045
 sk_psock_verdict_data_ready+0x12d/0x550 net/core/skmsg.c:1257
 __udp_enqueue_schedule_skb+0xc54/0x10b0 net/ipv4/udp.c:1789
 __udp_queue_rcv_skb net/ipv4/udp.c:2346 [inline]
 udp_queue_rcv_one_skb+0xac5/0x19c0 net/ipv4/udp.c:2475
 __udp4_lib_mcast_deliver+0xc06/0xcf0 net/ipv4/udp.c:2585
 __udp4_lib_rcv+0x10f6/0x2620 net/ipv4/udp.c:2724
 ip_protocol_deliver_rcu+0x282/0x440 net/ipv4/ip_input.c:207
 ip_local_deliver_finish+0x3bb/0x6f0 net/ipv4/ip_input.c:241
 NF_HOOK+0x336/0x3c0 include/linux/netfilter.h:318
 dst_input include/net/dst.h:474 [inline]
 ip_sublist_rcv_finish+0x221/0x2a0 net/ipv4/ip_input.c:584
 ip_list_rcv_finish net/ipv4/ip_input.c:628 [inline]
 ip_sublist_rcv+0x5c6/0xa70 net/ipv4/ip_input.c:644
 ip_list_rcv+0x3f1/0x450 net/ipv4/ip_input.c:678
 __netif_receive_skb_list_ptype net/core/dev.c:6195 [inline]
 __netif_receive_skb_list_core+0x7e5/0x810 net/core/dev.c:6242
 __netif_receive_skb_list net/core/dev.c:6294 [inline]
 netif_receive_skb_list_internal+0x995/0xcf0 net/core/dev.c:6385
 netif_receive_skb_list+0x54/0x410 net/core/dev.c:6437
 xdp_recv_frames net/bpf/test_run.c:269 [inline]
 xdp_test_run_batch net/bpf/test_run.c:350 [inline]
 bpf_test_run_xdp_live+0x1946/0x1cf0 net/bpf/test_run.c:379
 bpf_prog_test_run_xdp+0x81c/0x1160 net/bpf/test_run.c:1396
 bpf_prog_test_run+0x2c7/0x340 kernel/bpf/syscall.c:4703
 __sys_bpf+0x5cb/0x920 kernel/bpf/syscall.c:6182
 __do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6021:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2540 [inline]
 slab_free mm/slub.c:6674 [inline]
 kfree+0x1be/0x650 mm/slub.c:6882
 kfree_sk_msg include/linux/skmsg.h:385 [inline]
 sk_msg_recvmsg+0xaa8/0xc30 net/core/skmsg.c:483
 udp_bpf_recvmsg+0x4bd/0xe00 net/ipv4/udp_bpf.c:84
 inet_recvmsg+0x260/0x270 net/ipv4/af_inet.c:891
 sock_recvmsg_nosec net/socket.c:1078 [inline]
 sock_recvmsg+0x1a8/0x270 net/socket.c:1100
 ____sys_recvmsg+0x1e6/0x4a0 net/socket.c:2812
 ___sys_recvmsg+0x215/0x590 net/socket.c:2854
 do_recvmmsg+0x334/0x800 net/socket.c:2949
 __sys_recvmmsg net/socket.c:3023 [inline]
 __do_sys_recvmmsg net/socket.c:3046 [inline]
 __se_sys_recvmmsg net/socket.c:3039 [inline]
 __x64_sys_recvmmsg+0x198/0x250 net/socket.c:3039
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: 9f2470fbc4cb ("skmsg: Improve udp_bpf_recvmsg() accuracy")
Reported-by: syzbot+9307c991a6d07ce6e6d8@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/69922ac9.a70a0220.2c38d7.00e0.GAE@google.com/
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://lore.kernel.org/r/20260615021959.140010-5-jiayuan.chen@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/net/ipv4/udp_bpf.c b/net/ipv4/udp_bpf.c
index 9f33b07b148131929757f25daed85cbb15b84bad..ad57c4c9eaab6ff4f379f4625d530b15e087f658 100644 (file)
--- a/net/ipv4/udp_bpf.c
+++ b/net/ipv4/udp_bpf.c
@@ -50,7 +50,9 @@ static int udp_msg_wait_data(struct sock *sk, struct sk_psock *psock,
        sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
        ret = udp_msg_has_data(sk, psock);
        if (!ret) {
+               release_sock(sk);
                wait_woken(&wait, TASK_INTERRUPTIBLE, timeo);
+               lock_sock(sk);
                ret = udp_msg_has_data(sk, psock);
        }
        sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
@@ -79,6 +81,7 @@ static int udp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
                goto out;
        }
 
+       lock_sock(sk);
 msg_bytes_ready:
        copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
        if (!copied) {
@@ -90,11 +93,17 @@ msg_bytes_ready:
                if (data) {
                        if (psock_has_data(psock))
                                goto msg_bytes_ready;
+
+                       release_sock(sk);
+
                        ret = sk_udp_recvmsg(sk, msg, len, flags);
                        goto out;
                }
                copied = -EAGAIN;
        }
+
+       release_sock(sk);
+
        ret = copied;
 out:
        sk_psock_put(sk, psock);