On Thu Jun 11, 2026 at 8:34 AM EDT, Jiayuan Chen wrote: > From: Kuniyuki Iwashima <[email protected]> > > 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 accidentally 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: [email protected] > Closes: > https://lore.kernel.org/netdev/[email protected]/ > Reviewed-by: Jiayuan Chen <[email protected]> > Reviewed-by: Jakub Sitnicki <[email protected]>
Reviewed-by: Emil Tsalapatis <[email protected]> > Signed-off-by: Kuniyuki Iwashima <[email protected]> > Cc: Jiayuan Chen <[email protected]> > --- > net/ipv4/udp_bpf.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/net/ipv4/udp_bpf.c b/net/ipv4/udp_bpf.c > index 9f33b07b14813..ad57c4c9eaab6 100644 > --- 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 @@ static int udp_bpf_recvmsg(struct sock *sk, struct msghdr > *msg, size_t len, > 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);
