Merge branch 'atm-fix-uninit-and-mem-accounting-leak-in-vcc_sendmsg'

Kuniyuki Iwashima says:

====================
atm: Fix uninit and mem accounting leak in vcc_sendmsg().

Patch 1 fixes uninit issue reported by KMSAN, and patch 2 fixes
another issue found by Simon Horman during review for v1 patch.

v1: https://lore.kernel.org/20250613055700.415596-1-kuni1840@gmail.com
====================

Link: https://patch.msgid.link/20250616182147.963333-1-kuni1840@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

drivers/atm/atmtcp.c

@@ -288,7 +288,9 @@ static int atmtcp_c_send(struct atm_vcc *vcc,struct sk_buff *skb)
 	struct sk_buff *new_skb;
 	int result = 0;
 
-	if (!skb->len) return 0;
+	if (skb->len < sizeof(struct atmtcp_hdr))
+		goto done;
+
 	dev = vcc->dev_data;
 	hdr = (struct atmtcp_hdr *) skb->data;
 	if (hdr->length == ATMTCP_HDR_MAGIC) {

include/linux/atmdev.h

@@ -249,6 +249,12 @@ static inline void atm_account_tx(struct atm_vcc *vcc, struct sk_buff *skb)
 	ATM_SKB(skb)->atm_options = vcc->atm_options;
 }
 
+static inline void atm_return_tx(struct atm_vcc *vcc, struct sk_buff *skb)
+{
+	WARN_ON_ONCE(refcount_sub_and_test(ATM_SKB(skb)->acct_truesize,
+					   &sk_atm(vcc)->sk_wmem_alloc));
+}
+
 static inline void atm_force_charge(struct atm_vcc *vcc,int truesize)
 {
 	atomic_add(truesize, &sk_atm(vcc)->sk_rmem_alloc);

net/atm/common.c

@@ -635,6 +635,7 @@ int vcc_sendmsg(struct socket *sock, struct msghdr *m, size_t size)
 
 	skb->dev = NULL; /* for paths shared with net_device interfaces */
 	if (!copy_from_iter_full(skb_put(skb, size), size, &m->msg_iter)) {
+		atm_return_tx(vcc, skb);
 		kfree_skb(skb);
 		error = -EFAULT;
 		goto out;

net/atm/raw.c

@@ -36,7 +36,7 @@ static void atm_pop_raw(struct atm_vcc *vcc, struct sk_buff *skb)
 
 	pr_debug("(%d) %d -= %d\n",
 		 vcc->vci, sk_wmem_alloc_get(sk), ATM_SKB(skb)->acct_truesize);
-	WARN_ON(refcount_sub_and_test(ATM_SKB(skb)->acct_truesize, &sk->sk_wmem_alloc));
+	atm_return_tx(vcc, skb);
 	dev_kfree_skb_any(skb);
 	sk->sk_write_space(sk);
 }