vsock_check_source(9)

🌸 VSOCK_CHECK_SOURCE(9) 💅

okay so bestie, welcome to the Kernel API Manual — yes we're reading kernel manpages now, this is our era ✨ and today's main character is vsock_check_source(9), a tiny function with big "am I supposed to be here" energy 🎀

---

📛 NAME 📛

vsock_check_source — the vibe check for packets 💖 it validates whether a packet's source actually matches the socket's stored peer. no cap, it's just doing security door duty 🫶

---

✨ SYNOPSIS ✨

bool vsock_check_source (const struct vsock_sock *vsk , const struct
vsock_transport *transport , const struct sockaddr_vm *src );

look at her, three arguments, returns a bool, she's so clean, she's so iconic 👑

---

🧚 ARGUMENTS 🧚

• vsk — the socket that's receiving the packet, aka the one getting the mail 📬 (type: const struct vsock_sock *)
• transport — the transport that's receiving the packet, the delivery service in question 🚚 (type: const struct vsock_transport *)
• src — the source address pulled straight out of the packet, like checking the return address on an envelope ✉️ (type: const struct sockaddr_vm *)

---

🔥 RETURN 🔥

it returns true when both of these slay 💯:

1. the packet arrived on the socket's assigned transport, and
2. its source matches the stored peer 🫶

now for the loopback lore, because this part is lowkey important 👀: loopback packets are generated internally and they always use the local CID as their source — and yes, that includes connections that are using a valid CID alias 🌈. it's giving "internal mail doesn't need a stamp," iykyk.

if it's not both of those things, don't expect a true back, bestie 🙈

---

💀 DESCRIPTION 💀

two rules, and they're not optional, fr fr:

• the caller must hold the socket lock 🔒 do not skip this, this is the whole assignment
• do not call this for listening sockets 🚫👂 listening sockets accept packets from any source and have no assigned transport — so this check literally doesn't apply to them, it's not their moment

⚠️ seriously, the socket lock thing is not a suggestion. and the listening-socket thing is a must not, not a "prolly shouldn't" 😭

---

👑 SEE ALSO 👑

• Kernel file ./net/vmw_vsock/af_vsock.c — go read the source, she's right there, go be nosy 🦋

---

🌸 okay that's the whole page, you ate that 🍓 this diva lives in ./net/vmw_vsock and the calendar says October 2026 ⭐ periodt. now go hold that socket lock 💜🫶