From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp74.iad3b.emailsrvr.com (smtp74.iad3b.emailsrvr.com [146.20.161.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A4EB9210EC for ; Wed, 22 May 2024 18:42:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=146.20.161.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716403325; cv=none; b=og+67TnLWOmU1/KTXHMdmBuzFclRMEhxJk9aD+1OQ0/z2K8WEt2EXtdCr07wPR3UtY/g/sqbuvlUXGHKdV0b8SAaYlRqsAvmpoqPiUWKawvHw+k0DYcvDHQEy1ihVkk8+nCsjlnIg2Q38Jcs9n6V/PNP7f/mD6vD6MQ1rVmov/I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716403325; c=relaxed/simple; bh=ySNPFp42Pieo074fBKwdp9rOAjmYfFBiDHDybLRZ5yQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=eq8MdzPd0dkZFx07lkGQMO6i2HH0YkcLNGylH5GMWV+QwCJWnnYfOud4y4afHjWbkRi22G9t+FmYC6lXP5n3rtm1D4ALxwYmTu05OvH2x++AcHvgIRbuycX6nk2oDIJuXFWw4n/No5PAMMgOEXTD3z7tyxQoFi7q5aVs44SXPl0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=oddbit.com; spf=pass smtp.mailfrom=oddbit.com; dkim=pass (1024-bit key) header.d=oddbit.com header.i=@oddbit.com header.b=I1sOM9Yw; arc=none smtp.client-ip=146.20.161.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=oddbit.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oddbit.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=oddbit.com header.i=@oddbit.com header.b="I1sOM9Yw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=oddbit.com; s=20180920-g2b7aziw; t=1716402792; bh=ySNPFp42Pieo074fBKwdp9rOAjmYfFBiDHDybLRZ5yQ=; h=From:To:Subject:Date:From; b=I1sOM9YwNhBKkJHBauFg6rOU4OIqzluZ8nH+acyY8RdNrl/0NesBmWFmiryFMCSYX zxSk12F3GBBiQYc8Zt5NrBANuQM3XI6Kj3+2o9hi/5Vz9i/BQOt/TNEtx/rWe7CaC0 eUYsVSWbQQUxsOD1P68okQ9GiWJBjMrRXx/910T4= X-Auth-ID: lars@oddbit.com Received: by smtp18.relay.iad3b.emailsrvr.com (Authenticated sender: lars-AT-oddbit.com) with ESMTPSA id BB159E01A1; Wed, 22 May 2024 14:33:12 -0400 (EDT) From: lars@oddbit.com To: linux-hams@vger.kernel.org, netdev@vger.kernel.org Cc: Lars Kellogg-Stedman Subject: [PATCH v4] ax25: Fix refcount imbalance on inbound connections Date: Wed, 22 May 2024 14:31:34 -0400 Message-ID: <20240522183133.729159-2-lars@oddbit.com> X-Mailer: git-send-email 2.45.1 Precedence: bulk X-Mailing-List: linux-hams@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Classification-ID: f7386572-d13f-4673-a958-15858f2dedea-1-1 From: Lars Kellogg-Stedman When releasing a socket in ax25_release(), we call netdev_put() to decrease the refcount on the associated ax.25 device. However, the execution path for accepting an incoming connection never calls netdev_hold(). This imbalance leads to refcount errors, and ultimately to kernel crashes. A typical call trace for the above situation looks like this: Call Trace: ? show_regs+0x64/0x70 ? __warn+0x83/0x120 ? refcount_warn_saturate+0xb2/0x100 ? report_bug+0x158/0x190 ? prb_read_valid+0x20/0x30 ? handle_bug+0x3e/0x70 ? exc_invalid_op+0x1c/0x70 ? asm_exc_invalid_op+0x1f/0x30 ? refcount_warn_saturate+0xb2/0x100 ? refcount_warn_saturate+0xb2/0x100 ax25_release+0x2ad/0x360 __sock_release+0x35/0xa0 sock_close+0x19/0x20 [...] On reboot (or any attempt to remove the interface), the kernel gets stuck in an infinite loop: unregister_netdevice: waiting for ax0 to become free. Usage count = 0 This patch corrects these issues by ensuring that we call netdev_hold() and ax25_dev_hold() for new connections in ax25_accept(). Fixes: 7d8a3a477b ("ax25: Fix ax25 session cleanup problems") Signed-off-by: Lars Kellogg-Stedman --- v3: - Address naveenm's comments regarding the ordering of variable declarations (https://lore.kernel.org/netdev/SJ2PR18MB5635B7ADC7339BEDB79B183DA2EA2@SJ2PR18MB5635.namprd18.prod.outlook.com/) v4: - respond to kuba's comments regarding the Fixes: tag (https://lore.kernel.org/netdev/20240522100701.4d9edf99@kernel.org/) net/ax25/af_ax25.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index 8077cf2ee44..d6f9fae06a9 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -1378,8 +1378,10 @@ static int ax25_accept(struct socket *sock, struct socket *newsock, { struct sk_buff *skb; struct sock *newsk; + ax25_dev *ax25_dev; DEFINE_WAIT(wait); struct sock *sk; + ax25_cb *ax25; int err = 0; if (sock->state != SS_UNCONNECTED) @@ -1434,6 +1436,10 @@ static int ax25_accept(struct socket *sock, struct socket *newsock, kfree_skb(skb); sk_acceptq_removed(sk); newsock->state = SS_CONNECTED; + ax25 = sk_to_ax25(newsk); + ax25_dev = ax25->ax25_dev; + netdev_hold(ax25_dev->dev, &ax25->dev_tracker, GFP_ATOMIC); + ax25_dev_hold(ax25_dev); out: release_sock(sk); -- 2.45.1