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From: Kuniyuki Iwashima To: John Fastabend , Jakub Sitnicki Cc: Willem de Bruijn , Kuniyuki Iwashima , Kuniyuki Iwashima , bpf@vger.kernel.org, netdev@vger.kernel.org, syzbot+5b3b7e51dda1be027b7a@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" syzbot reported imbalanced sk->sk_forward_alloc [0] and demonstrated that UDP memory accounting by SOCKMAP is broken. The repro put a UDP sk into SOCKMAP and redirected skb to itself, where skb->truesize was 4240. First, udp_rmem_schedule() set sk->sk_forward_alloc to 8192 (2 * PAGE_SIZE), and skb->truesize was charged: sk->sk_forward_alloc = 0 + 8192 - 4240; // => 3952 Then, udp_read_skb() dequeued the skb by skb_recv_udp(), which finally calls udp_rmem_release() and _partially_ reclaims sk->sk_forward_alloc because skb->truesize was larger than PAGE_SIZE: sk->sk_forward_alloc += 4240; // => 8192 (PAGE_SIZE is reclaimable) sk->sk_forward_alloc -= 4096; // => 4096 Later, sk_psock_skb_ingress_self() called skb_set_owner_r() to charge the skb again, triggering an sk->sk_forward_alloc underflow: sk->sk_forward_alloc -= 4240 // => -144 Another problem is that UDP memory accounting is not performed under spin_lock_bh(&sk->sk_receive_queue.lock). skb_set_owner_r() and sock_rfree() are called locklessly and corrupt sk->sk_forward_alloc, leading to the splat. Let's not skip memory accounting for UDP and ensure the proper lock is held. [0]: WARNING: net/ipv4/af_inet.c:157 at inet_sock_destruct+0x62d/0x740 net/ipv4/af_inet.c:157, CPU#0: ksoftirqd/0/15 Modules linked in: CPU: 0 UID: 0 PID: 15 Comm: ksoftirqd/0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026 RIP: 0010:inet_sock_destruct+0x62d/0x740 net/ipv4/af_inet.c:157 Code: 0f 0b 90 e9 58 fe ff ff e8 40 55 b3 f7 90 0f 0b 90 e9 8b fe ff ff e8 32 55 b3 f7 90 0f 0b 90 e9 b1 fe ff ff e8 24 55 b3 f7 90 <0f> 0b 90 e9 d7 fe ff ff 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c 95 fc RSP: 0018:ffffc90000147a48 EFLAGS: 00010246 RAX: ffffffff8a1121dc RBX: dffffc0000000000 RCX: ffff88801d2c3d00 RDX: 0000000000000100 RSI: 0000000000000f70 RDI: 0000000000000000 RBP: 0000000000000f70 R08: ffff888030ce1327 R09: 1ffff1100619c264 R10: dffffc0000000000 R11: ffffed100619c265 R12: ffff888030ce1080 R13: dffffc0000000000 R14: ffff888030ce130c R15: ffffffff8fa87e00 FS: 0000000000000000(0000) GS:ffff8881256f8000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000700 CR3: 000000007200c000 CR4: 00000000003526f0 Call Trace: __sk_destruct+0x85/0x880 net/core/sock.c:2350 rcu_do_batch kernel/rcu/tree.c:2605 [inline] rcu_core+0xc9e/0x1750 kernel/rcu/tree.c:2857 handle_softirqs+0x22a/0x7c0 kernel/softirq.c:622 run_ksoftirqd+0x36/0x60 kernel/softirq.c:1063 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160 kthread+0x726/0x8b0 kernel/kthread.c:463 ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 Fixes: d7f571188ecf ("udp: Implement ->read_sock() for sockmap") Reported-by: syzbot+5b3b7e51dda1be027b7a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/698f84c6.a70a0220.2c38d7.00cb.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima --- v2: fix build failure when CONFIG_INET=n --- include/net/udp.h | 9 +++++++++ net/core/skmsg.c | 20 +++++++++++++++++--- net/ipv4/udp.c | 9 +++++++++ 3 files changed, 35 insertions(+), 3 deletions(-) diff --git a/include/net/udp.h b/include/net/udp.h index 700dbedcb15f..ae38a4da9388 100644 --- a/include/net/udp.h +++ b/include/net/udp.h @@ -455,6 +455,15 @@ struct sock *__udp6_lib_lookup(const struct net *net, struct sk_buff *skb); struct sock *udp6_lib_lookup_skb(const struct sk_buff *skb, __be16 sport, __be16 dport); + +#ifdef CONFIG_INET +void udp_sock_rfree(struct sk_buff *skb); +#else +static inline void udp_sock_rfree(struct sk_buff *skb) +{ +} +#endif + int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor); /* UDP uses skb->dev_scratch to cache as much information as possible and avoid diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 6bf3c517dbd2..c5fdb2827422 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -7,6 +7,7 @@ #include #include +#include #include #include @@ -576,6 +577,7 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb, u32 off, u32 len, gfp_t gfp_flags, bool take_ref) { struct sock *sk = psock->sk; + bool is_udp = sk_is_udp(sk); struct sk_msg *msg; int err = -EAGAIN; @@ -583,12 +585,15 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb, if (!msg) goto out; - if (skb->sk != sk) { + if (is_udp) + spin_lock_bh(&sk->sk_receive_queue.lock); + + if (skb->sk != sk || is_udp) { if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) - goto free; + goto unlock; if (!sk_rmem_schedule(sk, skb, skb->truesize)) - goto free; + goto unlock; } /* This is used in tcp_bpf_recvmsg_parser() to determine whether the @@ -606,11 +611,20 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb, */ skb_set_owner_r(skb, sk); + if (is_udp) { + skb->destructor = udp_sock_rfree; + spin_unlock_bh(&sk->sk_receive_queue.lock); + } + err = sk_psock_skb_ingress_enqueue(skb, off, len, psock, sk, msg, take_ref); if (err < 0) goto free; out: return err; + +unlock: + if (is_udp) + spin_unlock_bh(&sk->sk_receive_queue.lock); free: kfree(msg); goto out; diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 422c96fea249..831d26748a90 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -2039,6 +2039,15 @@ struct sk_buff *__skb_recv_udp(struct sock *sk, unsigned int flags, } EXPORT_SYMBOL(__skb_recv_udp); +void udp_sock_rfree(struct sk_buff *skb) +{ + struct sock *sk = skb->sk; + + spin_lock_bh(&sk->sk_receive_queue.lock); + sock_rfree(skb); + spin_unlock_bh(&sk->sk_receive_queue.lock); +} + int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor) { struct sk_buff *skb; -- 2.53.0.345.g96ddfc5eaa-goog