Message ID | 20230327175446.98151-2-john.fastabend@gmail.com (mailing list archive) |
---|---|
State | Superseded |
Delegated to: | BPF |
Headers | show |
Series | bpf sockmap fixes | expand |
On Mon, Mar 27, 2023 at 10:54 AM -07, John Fastabend wrote: > The read_skb hook calls consume_skb() now, but this means that if the > recv_actor program wants to use the skb it needs to inc the ref cnt > so that the consume_skb() doesn't kfree the sk_buff. > > This is problematic because in some error cases under memory pressure > we may need to linearize the sk_buff from sk_psock_skb_ingress_enqueue(). > Then we get this, > > skb_linearize() > __pskb_pull_tail() > pskb_expand_head() > BUG_ON(skb_shared(skb)) > > Because we incremented users refcnt from sk_psock_verdict_recv() we > hit the bug on with refcnt > 1 and trip it. > > To fix lets simply pass ownership of the sk_buff through the skb_read > call. Then we can drop the consume from read_skb handlers and assume > the verdict recv does any required kfree. > > Bug found while testing in our CI which runs in VMs that hit memory > constraints rather regularly. William tested TCP read_skb handlers. > > [ 106.536188] ------------[ cut here ]------------ > [ 106.536197] kernel BUG at net/core/skbuff.c:1693! > [ 106.536479] invalid opcode: 0000 [#1] PREEMPT SMP PTI > [ 106.536726] CPU: 3 PID: 1495 Comm: curl Not tainted 5.19.0-rc5 #1 > [ 106.537023] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ArchLinux 1.16.0-1 04/01/2014 > [ 106.537467] RIP: 0010:pskb_expand_head+0x269/0x330 > [ 106.538585] RSP: 0018:ffffc90000138b68 EFLAGS: 00010202 > [ 106.538839] RAX: 000000000000003f RBX: ffff8881048940e8 RCX: 0000000000000a20 > [ 106.539186] RDX: 0000000000000002 RSI: 0000000000000000 RDI: ffff8881048940e8 > [ 106.539529] RBP: ffffc90000138be8 R08: 00000000e161fd1a R09: 0000000000000000 > [ 106.539877] R10: 0000000000000018 R11: 0000000000000000 R12: ffff8881048940e8 > [ 106.540222] R13: 0000000000000003 R14: 0000000000000000 R15: ffff8881048940e8 > [ 106.540568] FS: 00007f277dde9f00(0000) GS:ffff88813bd80000(0000) knlGS:0000000000000000 > [ 106.540954] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 106.541227] CR2: 00007f277eeede64 CR3: 000000000ad3e000 CR4: 00000000000006e0 > [ 106.541569] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 106.541915] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 106.542255] Call Trace: > [ 106.542383] <IRQ> > [ 106.542487] __pskb_pull_tail+0x4b/0x3e0 > [ 106.542681] skb_ensure_writable+0x85/0xa0 > [ 106.542882] sk_skb_pull_data+0x18/0x20 > [ 106.543084] bpf_prog_b517a65a242018b0_bpf_skskb_http_verdict+0x3a9/0x4aa9 > [ 106.543536] ? migrate_disable+0x66/0x80 > [ 106.543871] sk_psock_verdict_recv+0xe2/0x310 > [ 106.544258] ? sk_psock_write_space+0x1f0/0x1f0 > [ 106.544561] tcp_read_skb+0x7b/0x120 > [ 106.544740] tcp_data_queue+0x904/0xee0 > [ 106.544931] tcp_rcv_established+0x212/0x7c0 > [ 106.545142] tcp_v4_do_rcv+0x174/0x2a0 > [ 106.545326] tcp_v4_rcv+0xe70/0xf60 > [ 106.545500] ip_protocol_deliver_rcu+0x48/0x290 > [ 106.545744] ip_local_deliver_finish+0xa7/0x150 > > Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()") > Reported-by: William Findlay <will@isovalent.com> > Tested-by: William Findlay <will@isovalent.com> > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > --- Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 53d0251788aa..2b6d9519ff29 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -1180,8 +1180,6 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb) int ret = __SK_DROP; int len = skb->len; - skb_get(skb); - rcu_read_lock(); psock = sk_psock(sk); if (unlikely(!psock)) { diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 33f559f491c8..6572962b0237 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1770,7 +1770,6 @@ int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor) WARN_ON_ONCE(!skb_set_owner_sk_safe(skb, sk)); tcp_flags = TCP_SKB_CB(skb)->tcp_flags; used = recv_actor(sk, skb); - consume_skb(skb); if (used < 0) { if (!copied) copied = used; diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 9592fe3e444a..04e8c6385246 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1832,10 +1832,7 @@ int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor) } WARN_ON_ONCE(!skb_set_owner_sk_safe(skb, sk)); - copied = recv_actor(sk, skb); - kfree_skb(skb); - - return copied; + return recv_actor(sk, skb); } EXPORT_SYMBOL(udp_read_skb); diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index f0c2293f1d3b..a5dd2ee0cfed 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -2554,10 +2554,7 @@ static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor) if (!skb) return err; - copied = recv_actor(sk, skb); - kfree_skb(skb); - - return copied; + return recv_actor(sk, skb); } /*