| Message ID | 20260204141441.528655-1-ralf@mandelbit.com |
|---|---|
| State | New |
| Headers | show |
| Series | [Openvpn-devel,ovpn,net] ovpn: tcp - fix packet extraction from stream | expand |
On Wed, 2026-02-04 at 15:14 +0100, Ralf Lici wrote: > When processing TCP stream data in ovpn_tcp_recv, we receive large > cloned skbs from __strp_rcv that may contain multiple coalesced > packets. > The current implementation has two bugs: > > 1. Header offset overflow: Using pskb_pull with large offsets on > coalesced skbs causes skb->data - skb->head to exceed the u16 > storage > of skb->network_header. This causes skb_reset_network_header to > fail > on the inner decapsulated packet, resulting in packet drops. > > 2. Unaligned protocol headers: Extracting packets from arbitrary > positions within the coalesced TCP stream provides no alignment > guarantees for the packet data causing performance penalties on > architectures without efficient unaligned access. Additionally, > openvpn's 2-byte length prefix on TCP packets causes the subsequent > 4-byte opcode and packet ID fields to be inherently misaligned. > > Fix both issues by allocating a new skb for each openvpn packet and > using skb_copy_bits to extract only the packet content into the new > buffer, skipping the 2-byte length prefix. Also, check the length > before > invoking the function that performs the allocation to avoid creating > an > invalid skb. > > If the packet has to be forwarded to userspace the 2-byte prefix can > be > pushed to the head safely, without misalignment. > > As a side effect, this approach also avoids the expensive > linearization > that pskb_pull triggers on cloned skbs with page fragments. In > testing, > this resulted in TCP throughput improvements of up to 74%. > > Fixes: 11851cbd60ea ("ovpn: implement TCP transport") > Signed-off-by: Ralf Lici <ralf@mandelbit.com> > --- > drivers/net/ovpn/tcp.c | 53 ++++++++++++++++++++++++++++------------- > - > 1 file changed, 36 insertions(+), 17 deletions(-) > > diff --git a/drivers/net/ovpn/tcp.c b/drivers/net/ovpn/tcp.c > index b7348da9b040..ffe8db69d76d 100644 > --- a/drivers/net/ovpn/tcp.c > +++ b/drivers/net/ovpn/tcp.c > @@ -70,37 +70,56 @@ static void ovpn_tcp_to_userspace(struct ovpn_peer > *peer, struct sock *sk, > peer->tcp.sk_cb.sk_data_ready(sk); > } > > -static void ovpn_tcp_rcv(struct strparser *strp, struct sk_buff *skb) > +static struct sk_buff *ovpn_tcp_skb_packet(const struct ovpn_peer > *peer, > + struct sk_buff *orig_skb, > + const int pkt_len, const > int pkt_off) > { > - struct ovpn_peer *peer = container_of(strp, struct ovpn_peer, > tcp.strp); > - struct strp_msg *msg = strp_msg(skb); > - size_t pkt_len = msg->full_len - 2; > - size_t off = msg->offset + 2; > - u8 opcode; > + struct sk_buff *ovpn_skb; > + int err; > > - /* ensure skb->data points to the beginning of the openvpn > packet */ > - if (!pskb_pull(skb, off)) { > - net_warn_ratelimited("%s: packet too small for peer > %u\n", > - netdev_name(peer->ovpn->dev), > peer->id); > + /* create a new skb with only the content of the current > packet */ > + ovpn_skb = netdev_alloc_skb(peer->ovpn->dev, pkt_len); > + if (unlikely(!ovpn_skb)) > goto err; > - } > > - /* strparser does not trim the skb for us, therefore we do it > now */ > - if (pskb_trim(skb, pkt_len) != 0) { > - net_warn_ratelimited("%s: trimming skb failed for > peer %u\n", > + skb_copy_header(ovpn_skb, orig_skb); > + err = skb_copy_bits(orig_skb, pkt_off, skb_put(ovpn_skb, > pkt_len), > + pkt_len); > + if (unlikely(err)) { > + net_warn_ratelimited("%s: skb_copy_bits failed for > peer %u\n", > netdev_name(peer->ovpn->dev), > peer->id); > + kfree_skb(ovpn_skb); > goto err; > } > > - /* we need the first 4 bytes of data to be accessible > + consume_skb(orig_skb); > + return ovpn_skb; > +err: > + kfree_skb(orig_skb); > + return NULL; > +} > + > +static void ovpn_tcp_rcv(struct strparser *strp, struct sk_buff *skb) > +{ > + struct ovpn_peer *peer = container_of(strp, struct ovpn_peer, > tcp.strp); > + struct strp_msg *msg = strp_msg(skb); > + int pkt_len = msg->full_len - 2; > + u8 opcode; > + > + /* we need at least 4 bytes of data in the packet > * to extract the opcode and the key ID later on > */ > - if (!pskb_may_pull(skb, OVPN_OPCODE_SIZE)) { > + if (unlikely(pkt_len < OVPN_OPCODE_SIZE)) { > net_warn_ratelimited("%s: packet too small to fetch > opcode for peer %u\n", > netdev_name(peer->ovpn->dev), > peer->id); > goto err; > } > > + /* extract the packet into a new skb */ > + skb = ovpn_tcp_skb_packet(peer, skb, pkt_len, msg->offset + > 2); > + if (unlikely(!skb)) > + goto err; > + > /* DATA_V2 packets are handled in kernel, the rest goes to > user space */ > opcode = ovpn_opcode_from_skb(skb, 0); > if (unlikely(opcode != OVPN_DATA_V2)) { > @@ -113,7 +132,7 @@ static void ovpn_tcp_rcv(struct strparser *strp, > struct sk_buff *skb) > /* The packet size header must be there when sending > the packet > * to userspace, therefore we put it back > */ > - skb_push(skb, 2); > + *((__force __be16 *)__skb_push(skb, 2)) = > cpu_to_be16(pkt_len); > ovpn_tcp_to_userspace(peer, strp->sk, skb); > return; > } This issue manifests as the following warning (on skb_reset_network_header): [ 126.764066] ------------[ cut here ]------------ [ 126.764541] WARNING: CPU: 1 PID: 22 at ./include/linux/skbuff.h:3122 ovpn_decrypt_post+0x531/0x7b0 [ovpn] [ 126.765698] Modules linked in: ovpn ip6_udp_tunnel udp_tunnel chacha libchacha chacha20poly1305 libpoly1305 veth [last unloaded: ip6_udp_tunnel] [ 126.767085] CPU: 1 UID: 0 PID: 22 Comm: ksoftirqd/1 Not tainted 6.17.0+ #222 PREEMPT(none) [ 126.768053] RIP: 0010:ovpn_decrypt_post+0x531/0x7b0 [ovpn] [ 126.768769] Code: cc cc cc cc 48 2b 93 c8 00 00 00 83 c2 28 0f 88 62 02 00 00 89 c8 29 f0 39 d0 0f 82 2e 02 00 00 b8 86 dd ff ff e9 68 fe ff ff <0f> 0b e9 20 fc ff ff 0f 0b e9 35 fc ff ff 39 c1 0f 82 5b fc ff ff [ 126.770834] RSP: 0018:ffffc900000d77f0 EFLAGS: 00010216 [ 126.771503] RAX: 000000000001034c RBX: ffff88810c7ac100 RCX: 0000000000000588 [ 126.772386] RDX: ffff888116ee0000 RSI: 0000000000000000 RDI: ffffffff8359f040 [ 126.773251] RBP: ffffc900000d7820 R08: 00000000000005a0 R09: ffff888116ef034c [ 126.774126] R10: 0000000000000000 R11: 0000000000000001 R12: ffff888116bec800 [ 126.774980] R13: ffff888108118000 R14: 0000000000000018 R15: ffff888103a6cc00 [ 126.775871] FS: 0000000000000000(0000) GS:ffff8882f446b000(0000) knlGS:0000000000000000 [ 126.776839] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 126.777605] CR2: 00007f5f9d2fc000 CR3: 000000011659b000 CR4: 0000000000750eb0 [ 126.778434] PKRU: 55555554 [ 126.778887] Call Trace: [ 126.779324] <TASK> [ 126.779728] ovpn_recv+0x15b/0x3a0 [ovpn] [ 126.780299] ovpn_tcp_rcv+0xbd/0x320 [ovpn] [ 126.780886] __strp_recv+0x172/0x640 [ 126.781430] strp_recv+0x27/0x30 [ 126.781931] __tcp_read_sock+0x92/0x260 [ 126.782483] ? __pfx_strp_recv+0x10/0x10 [ 126.783055] tcp_read_sock+0x1b/0x30 [ 126.783586] strp_read_sock+0xce/0xe0 [ 126.784162] strp_data_ready+0x6a/0xa0 [ 126.784721] ovpn_tcp_data_ready+0x90/0x220 [ovpn] [ 126.785441] tcp_data_ready+0x30/0xd0 [ 126.785992] tcp_data_queue+0x8a4/0x1000 [ 126.786560] tcp_rcv_established+0x328/0xca0 [ 126.787170] tcp_v4_do_rcv+0x18f/0x3c0 [ 126.787726] tcp_v4_rcv+0xf51/0x1520 [ 126.788264] ip_protocol_deliver_rcu+0x4a/0x200 [ 126.788898] ? process_backlog+0x14b/0x630 [ 126.789552] ip_local_deliver_finish+0xd7/0x220 [ 126.790193] ip_local_deliver+0x63/0x250 [ 126.790769] ? lock_is_held_type+0x9c/0x110 [ 126.791366] ? process_backlog+0x14b/0x630 [ 126.791995] ip_rcv+0x26f/0x340 [ 126.792516] ? process_backlog+0x14b/0x630 [ 126.793114] ? process_backlog+0x14b/0x630 [ 126.793714] __netif_receive_skb_one_core+0x6b/0x80 [ 126.794358] __netif_receive_skb+0x16/0x60 [ 126.794951] process_backlog+0x18b/0x630 [ 126.795515] ? process_backlog+0x6a/0x630 [ 126.796109] __napi_poll.constprop.0+0x2e/0x1e0 [ 126.796721] net_rx_action+0x384/0x420 [ 126.797252] ? local_clock_noinstr+0x13/0xf0 [ 126.797861] handle_softirqs+0xc8/0x3f0 [ 126.798401] ? __pfx_smpboot_thread_fn+0x10/0x10 [ 126.799024] run_ksoftirqd+0x36/0x50 [ 126.799548] smpboot_thread_fn+0xfe/0x230 [ 126.800110] kthread+0x103/0x210 [ 126.800602] ? __pfx_kthread+0x10/0x10 [ 126.801145] ret_from_fork+0x18a/0x1e0 [ 126.801705] ? __pfx_kthread+0x10/0x10 [ 126.802284] ret_from_fork_asm+0x1a/0x30 [ 126.802879] </TASK> [ 126.803288] irq event stamp: 41024 [ 126.803799] hardirqs last enabled at (41032): [<ffffffff8137676c>] __up_console_sem+0x5c/0x70 [ 126.804799] hardirqs last disabled at (41039): [<ffffffff81376751>] __up_console_sem+0x41/0x70 [ 126.805812] softirqs last enabled at (33936): [<ffffffff812e6486>] run_ksoftirqd+0x36/0x50 [ 126.806819] softirqs last disabled at (33941): [<ffffffff812e6486>] run_ksoftirqd+0x36/0x50 [ 126.807822] ---[ end trace 0000000000000000 ]---
diff --git a/drivers/net/ovpn/tcp.c b/drivers/net/ovpn/tcp.c index b7348da9b040..ffe8db69d76d 100644 --- a/drivers/net/ovpn/tcp.c +++ b/drivers/net/ovpn/tcp.c @@ -70,37 +70,56 @@ static void ovpn_tcp_to_userspace(struct ovpn_peer *peer, struct sock *sk, peer->tcp.sk_cb.sk_data_ready(sk); } -static void ovpn_tcp_rcv(struct strparser *strp, struct sk_buff *skb) +static struct sk_buff *ovpn_tcp_skb_packet(const struct ovpn_peer *peer, + struct sk_buff *orig_skb, + const int pkt_len, const int pkt_off) { - struct ovpn_peer *peer = container_of(strp, struct ovpn_peer, tcp.strp); - struct strp_msg *msg = strp_msg(skb); - size_t pkt_len = msg->full_len - 2; - size_t off = msg->offset + 2; - u8 opcode; + struct sk_buff *ovpn_skb; + int err; - /* ensure skb->data points to the beginning of the openvpn packet */ - if (!pskb_pull(skb, off)) { - net_warn_ratelimited("%s: packet too small for peer %u\n", - netdev_name(peer->ovpn->dev), peer->id); + /* create a new skb with only the content of the current packet */ + ovpn_skb = netdev_alloc_skb(peer->ovpn->dev, pkt_len); + if (unlikely(!ovpn_skb)) goto err; - } - /* strparser does not trim the skb for us, therefore we do it now */ - if (pskb_trim(skb, pkt_len) != 0) { - net_warn_ratelimited("%s: trimming skb failed for peer %u\n", + skb_copy_header(ovpn_skb, orig_skb); + err = skb_copy_bits(orig_skb, pkt_off, skb_put(ovpn_skb, pkt_len), + pkt_len); + if (unlikely(err)) { + net_warn_ratelimited("%s: skb_copy_bits failed for peer %u\n", netdev_name(peer->ovpn->dev), peer->id); + kfree_skb(ovpn_skb); goto err; } - /* we need the first 4 bytes of data to be accessible + consume_skb(orig_skb); + return ovpn_skb; +err: + kfree_skb(orig_skb); + return NULL; +} + +static void ovpn_tcp_rcv(struct strparser *strp, struct sk_buff *skb) +{ + struct ovpn_peer *peer = container_of(strp, struct ovpn_peer, tcp.strp); + struct strp_msg *msg = strp_msg(skb); + int pkt_len = msg->full_len - 2; + u8 opcode; + + /* we need at least 4 bytes of data in the packet * to extract the opcode and the key ID later on */ - if (!pskb_may_pull(skb, OVPN_OPCODE_SIZE)) { + if (unlikely(pkt_len < OVPN_OPCODE_SIZE)) { net_warn_ratelimited("%s: packet too small to fetch opcode for peer %u\n", netdev_name(peer->ovpn->dev), peer->id); goto err; } + /* extract the packet into a new skb */ + skb = ovpn_tcp_skb_packet(peer, skb, pkt_len, msg->offset + 2); + if (unlikely(!skb)) + goto err; + /* DATA_V2 packets are handled in kernel, the rest goes to user space */ opcode = ovpn_opcode_from_skb(skb, 0); if (unlikely(opcode != OVPN_DATA_V2)) { @@ -113,7 +132,7 @@ static void ovpn_tcp_rcv(struct strparser *strp, struct sk_buff *skb) /* The packet size header must be there when sending the packet * to userspace, therefore we put it back */ - skb_push(skb, 2); + *((__force __be16 *)__skb_push(skb, 2)) = cpu_to_be16(pkt_len); ovpn_tcp_to_userspace(peer, strp->sk, skb); return; }
When processing TCP stream data in ovpn_tcp_recv, we receive large cloned skbs from __strp_rcv that may contain multiple coalesced packets. The current implementation has two bugs: 1. Header offset overflow: Using pskb_pull with large offsets on coalesced skbs causes skb->data - skb->head to exceed the u16 storage of skb->network_header. This causes skb_reset_network_header to fail on the inner decapsulated packet, resulting in packet drops. 2. Unaligned protocol headers: Extracting packets from arbitrary positions within the coalesced TCP stream provides no alignment guarantees for the packet data causing performance penalties on architectures without efficient unaligned access. Additionally, openvpn's 2-byte length prefix on TCP packets causes the subsequent 4-byte opcode and packet ID fields to be inherently misaligned. Fix both issues by allocating a new skb for each openvpn packet and using skb_copy_bits to extract only the packet content into the new buffer, skipping the 2-byte length prefix. Also, check the length before invoking the function that performs the allocation to avoid creating an invalid skb. If the packet has to be forwarded to userspace the 2-byte prefix can be pushed to the head safely, without misalignment. As a side effect, this approach also avoids the expensive linearization that pskb_pull triggers on cloned skbs with page fragments. In testing, this resulted in TCP throughput improvements of up to 74%. Fixes: 11851cbd60ea ("ovpn: implement TCP transport") Signed-off-by: Ralf Lici <ralf@mandelbit.com> --- drivers/net/ovpn/tcp.c | 53 ++++++++++++++++++++++++++++-------------- 1 file changed, 36 insertions(+), 17 deletions(-)