From nobody Thu Apr 9 12:06:19 2026 Received: from mail-oo1-f70.google.com (mail-oo1-f70.google.com [209.85.161.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D6120221DB6 for ; Mon, 9 Mar 2026 06:28:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.70 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773037702; cv=none; b=lrxMGyJl2KTg15yt77IfvL91Fd52eCBa2ymClJ+ctcj6rFxsIOMxYnwrcCVMMffHJwBxRzvafmIgiNhTkM/27/YqbVs3X6fzMMgWB3hZ4EYQO1Z8eU2iyVqL0zWhI8fB27FVN6qKmOAd3tFUBH3pNa6+WtlNQPyAlq1AJrXfh6k= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773037702; c=relaxed/simple; bh=RSNECjlgnfgB9+OwiBeAKkvgniS+mPDTRDcPQ0uEfg8=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=PI8UXJ7lIvf1GGe04MhEPlWLX3V0UQDGN+yZDFDWeBSJvSXmUrzzdQG1Mamu36IMcbcX55MDcu6b1nfiEM4Idfo8dCzUV97PsWULR2AeA9ZxPyfSvII0CuZbmCC4YBFYWIvioaNaKQq9VcN36wmeMCCOXgK3iKgQwCSTFZhbrq8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.161.70 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oo1-f70.google.com with SMTP id 006d021491bc7-67bb376f013so5912422eaf.3 for ; Sun, 08 Mar 2026 23:28:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1773037700; x=1773642500; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=IHN7Zbhr9JKeE4Ci70X93h3xBqN7NosntKTxsD0L3xU=; b=sYMzwOp6TQzf17dNBO4BF0+PW36Ajm5bkyyo3z69lKNXBzIru3GZ2WU1/Asft7nCar YPugelGbjAZSvAxz3C/59qud2T56F7+DcuPQBVR0WSEf7CXcKkg+hM8TBBTX7vrzHRk7 TxbySyOGL38VAkedtbWRNuATUe/tQz//2OmU7jcWcbGmym7YCeg5FwU1SEHhUC8KNukb 9gP1o4UNS5J5wOHcVK1WCBawrepACF366400NoyOLLyiLeDqudkJUZc7G+kjaYpTYIeB 9/T0JYR+O8zTXLqhuKTbvV74DD4QPSSuP+Vm/PajxuxVgqajv1vHa5eqa0gBJbeBOtw2 5arQ== X-Gm-Message-State: AOJu0YyIq9M9gNP+caKOUB+ujvzFkhpp4HlSR+eBEsNuzXBVpV6mKfBT /DamghZel1CiQicHWIvTkdogZiJqwfb7aL27oHYjiZ49VbesuGfz9/3tdkXpbXafp8tzXAbdxJ7 u1Yr0yZLaSiKSSKw82jqY+AoGPe+TiezkBO3Xnwawq76TxUaG4iWL/OrUsS8= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:2910:b0:67b:b337:d430 with SMTP id 006d021491bc7-67bb337dd72mr1972838eaf.63.1773037699912; Sun, 08 Mar 2026 23:28:19 -0700 (PDT) Date: Sun, 08 Mar 2026 23:28:19 -0700 In-Reply-To: <69ad7ccb.a00a0220.b130.0003.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <69ae6883.a70a0220.52840.000e.GAE@google.com> Subject: Forwarded: [PATCH] atm: lec: fix use-after-free in sock_def_readable() From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] atm: lec: fix use-after-free in sock_def_readable() Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master A race condition exists between lec_atm_close() setting priv->lecd =3D NULL and concurrent access to priv->lecd in send_to_lecd(), lec_handle_bridge(), and lec_atm_send(). When the socket is freed via RCU while another thread is still using it, a use-after-free occurs in sock_def_readable() when accessing the socket's wait queue. The root cause is that lec_atm_close() clears priv->lecd without holding lec_arp_lock, while callers dereference priv->lecd without any protection against concurrent teardown. Fix this by: - Protecting priv->lecd =3D NULL in lec_atm_close() with lec_arp_lock to synchronize with callers that already hold the lock (e.g. lec_arp_resolve) - Using sock_hold/sock_put in send_to_lecd() to pin the socket while in use. This is safe because send_to_lecd() is called under lec_arp_lock by lec_arp_resolve(), preventing concurrent NULL assignment of lecd. - Using lec_arp_lock + sock_hold/sock_put in lec_handle_bridge() and lec_atm_send() where the lock is not held by the caller, with proper skb cleanup on early exit to avoid memory leaks. Reported-by: syzbot+f50072212ab792c86925@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Df50072212ab792c86925 Signed-off-by: Deepanshu Kartikey --- net/atm/lec.c | 31 +++++++++++++++++++++++++++---- 1 file changed, 27 insertions(+), 4 deletions(-) diff --git a/net/atm/lec.c b/net/atm/lec.c index fb93c6e1c329..7e051174a92b 100644 --- a/net/atm/lec.c +++ b/net/atm/lec.c @@ -131,6 +131,7 @@ static void lec_handle_bridge(struct sk_buff *skb, stru= ct net_device *dev) { char *buff; struct lec_priv *priv; + unsigned long flags; =20 /* * Check if this is a BPDU. If so, ask zeppelin to send @@ -154,10 +155,19 @@ static void lec_handle_bridge(struct sk_buff *skb, st= ruct net_device *dev) /* 0x01 is topology change */ =20 priv =3D netdev_priv(dev); - atm_force_charge(priv->lecd, skb2->truesize); + spin_lock_irqsave(&priv->lec_arp_lock, flags); + if (!priv->lecd) { + spin_unlock_irqrestore(&priv->lec_arp_lock, flags); + kfree_skb(skb2); + return; + } sk =3D sk_atm(priv->lecd); + sock_hold(sk); + spin_unlock_irqrestore(&priv->lec_arp_lock, flags); + atm_force_charge(priv->lecd, skb2->truesize); skb_queue_tail(&sk->sk_receive_queue, skb2); sk->sk_data_ready(sk); + sock_put(sk); } } #endif /* IS_ENABLED(CONFIG_BRIDGE) */ @@ -441,7 +451,7 @@ static int lec_atm_send(struct atm_vcc *vcc, struct sk_= buff *skb) /* hit from bridge table, send LE_ARP_RESPONSE */ struct sk_buff *skb2; struct sock *sk; - + unsigned long flags; pr_debug("%s: entry found, responding to zeppelin\n", dev->name); skb2 =3D alloc_skb(sizeof(struct atmlec_msg), GFP_ATOMIC); @@ -449,10 +459,19 @@ static int lec_atm_send(struct atm_vcc *vcc, struct s= k_buff *skb) break; skb2->len =3D sizeof(struct atmlec_msg); skb_copy_to_linear_data(skb2, mesg, sizeof(*mesg)); - atm_force_charge(priv->lecd, skb2->truesize); + spin_lock_irqsave(&priv->lec_arp_lock, flags); + if (!priv->lecd) { + spin_unlock_irqrestore(&priv->lec_arp_lock, flags); + kfree_skb(skb2); + break; + } sk =3D sk_atm(priv->lecd); + sock_hold(sk); + spin_unlock_irqrestore(&priv->lec_arp_lock, flags); + atm_force_charge(priv->lecd, skb2->truesize); skb_queue_tail(&sk->sk_receive_queue, skb2); sk->sk_data_ready(sk); + sock_put(sk); } } #endif /* IS_ENABLED(CONFIG_BRIDGE) */ @@ -471,8 +490,11 @@ static void lec_atm_close(struct atm_vcc *vcc) struct sk_buff *skb; struct net_device *dev =3D (struct net_device *)vcc->proto_data; struct lec_priv *priv =3D netdev_priv(dev); + unsigned long flags; =20 + spin_lock_irqsave(&priv->lec_arp_lock, flags); priv->lecd =3D NULL; + spin_unlock_irqrestore(&priv->lec_arp_lock, flags); /* Do something needful? */ =20 netif_stop_queue(dev); @@ -534,6 +556,7 @@ send_to_lecd(struct lec_priv *priv, atmlec_msg_type typ= e, =20 atm_force_charge(priv->lecd, skb->truesize); sk =3D sk_atm(priv->lecd); + sock_hold(sk); skb_queue_tail(&sk->sk_receive_queue, skb); sk->sk_data_ready(sk); =20 @@ -543,7 +566,7 @@ send_to_lecd(struct lec_priv *priv, atmlec_msg_type typ= e, skb_queue_tail(&sk->sk_receive_queue, data); sk->sk_data_ready(sk); } - + sock_put(sk); return 0; } =20 --=20 2.43.0