From nobody Wed Apr 1 14:04:51 2026 Received: from mxout70.expurgate.net (mxout70.expurgate.net [194.37.255.70]) (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 36D413CCFA9; Tue, 31 Mar 2026 07:43:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.37.255.70 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774943028; cv=none; b=mIAVA3MUTShjB4EiRmkPXhEBayFBs3PLY0wDF/Ff8ZjQzx8+k7V+tRhtsYsOqeHwYSSVG6rgLpjnkNVzsu3Ht+EgUF0HgjmDlSKiIpHnlT+7BEr3/Z7p3CGex0jsdCUbGnTc8Lx/2ZItkCvJxUIVyJsz0/ry2ph5J0XGOUGEoPU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774943028; c=relaxed/simple; bh=OdWsXOSpKx2KIVeAFa5xlYv3FnOYDsT/6PebGCuKocA=; h=From:Date:Subject:MIME-Version:Content-Type:Message-ID:References: In-Reply-To:To:Cc; b=kvfqPIJhi48hkzzno6VSTvdtPL2rovDjiUN+6h160/ZGhNbwxy94VeqIFOyWAsQEZyyADna386WAP2dT4/47He857F6+jLijesBk0lnl9vX+fyDIJIenjl/HOpHTXHDQuwuo6G8o1cW/bjfIGO+gFuLgydAF+NESF5iXcsbkdBY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=dev.tdt.de; spf=pass smtp.mailfrom=dev.tdt.de; dkim=temperror (0-bit key) header.d=dev.tdt.de header.i=@dev.tdt.de header.b=QfWikLGY; arc=none smtp.client-ip=194.37.255.70 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=dev.tdt.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=dev.tdt.de Authentication-Results: smtp.subspace.kernel.org; dkim=temperror (0-bit key) header.d=dev.tdt.de header.i=@dev.tdt.de header.b="QfWikLGY" Received: from [194.37.255.9] (helo=mxout.expurgate.net) by relay.expurgate.net with smtp (Exim 4.92) (envelope-from ) id 1w7Tl6-00FWkB-62; Tue, 31 Mar 2026 09:43:32 +0200 Received: from [195.243.126.94] (helo=securemail.tdt.de) by relay.expurgate.net with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1w7Tl4-006L8s-V4; Tue, 31 Mar 2026 09:43:31 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=dev.tdt.de; s=z1-selector1; t=1774943010; bh=RoA2ct3WGvm4MFq2PE1vvrax7TpOpLDv7PngWSXsJPI=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=QfWikLGYlZjty08nrUgN0MWu8fyHfsBw950JpsJFArDkr3ZFVXVQ6fzH76fazc3YV QcH3+op8j0xiVK+eLkiFm/L3X6c58ipcrgL4TSIxnNVqA1zKaOGjX2FXyQcl5fq8Si blLyKkA5JLiBXn3TI+NM6888/Q8rewa1qZmjpfd9U230B0lGhc4gDftAcZcz4TbrHt gPcdC9u0Kr4rM8FmtvazwPnibxKgwBRzA8a2c+oPHW31XRmyyZCNofx29lwMUikiLQ y+/in/SN4QQgW6suar8ZPZyJlF/Lxrs77y8GQVne0qPE9SFIwJ7XgBYZF8mAWjPfuy ee/njllylUzfg== Received: from securemail.tdt.de (localhost [127.0.0.1]) by securemail.tdt.de (Postfix) with ESMTP id 62A0D240042; Tue, 31 Mar 2026 09:43:30 +0200 (CEST) Received: from mail.dev.tdt.de (unknown [10.2.4.42]) by securemail.tdt.de (Postfix) with ESMTP id 4A744240040; Tue, 31 Mar 2026 09:43:30 +0200 (CEST) Received: from [127.0.1.1] (unknown [10.2.3.19]) by mail.dev.tdt.de (Postfix) with ESMTPSA id 2FE8821989; Tue, 31 Mar 2026 09:43:30 +0200 (CEST) From: Martin Schiller Date: Tue, 31 Mar 2026 09:43:17 +0200 Subject: [PATCH net v4 1/2] net/x25: Fix potential double free of skb Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-ID: <20260331-x25_fraglen-v4-1-3e69f18464b4@dev.tdt.de> References: <20260331-x25_fraglen-v4-0-3e69f18464b4@dev.tdt.de> In-Reply-To: <20260331-x25_fraglen-v4-0-3e69f18464b4@dev.tdt.de> To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: Yiming Qian , linux-x25@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, security@kernel.org, Martin Schiller X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1774943009; l=1460; i=ms@dev.tdt.de; s=20260220; h=from:subject:message-id; bh=OdWsXOSpKx2KIVeAFa5xlYv3FnOYDsT/6PebGCuKocA=; b=e51TX5V2EIvzzl0DONlvncVMtdme6hep7B3EFNgU2CRWaZyCC/OM1WniHet2gNgW/Blw8tV2J +XP26y0Nmn7BQv50uI5nEO5dSLEaVE/osiPCfmEmtJY+7eHF8y8v15w X-Developer-Key: i=ms@dev.tdt.de; a=ed25519; pk=MAojd7D5IafMnqCYSFC7hY/u/jppX58CLIEhsEsSOYE= X-purgate-type: clean X-purgate-ID: 151534::1774943011-43C75BD0-9040426B/0/0 X-purgate: clean When alloc_skb fails in x25_queue_rx_frame it calls kfree_skb(skb) at line 48 and returns 1 (error). This error propagates back through the call chain: x25_queue_rx_frame returns 1 | v x25_state3_machine receives the return value 1 and takes the else branch at line 278, setting queued=3D0 and returning 0 | v x25_process_rx_frame returns queued=3D0 | v x25_backlog_rcv at line 452 sees queued=3D0 and calls kfree_skb(skb) again This would free the same skb twice. Looking at x25_backlog_rcv: net/x25/x25_in.c:x25_backlog_rcv() { ... queued =3D x25_process_rx_frame(sk, skb); ... if (!queued) kfree_skb(skb); } Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Martin Schiller --- net/x25/x25_in.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/x25/x25_in.c b/net/x25/x25_in.c index b981a4828d08c2e6676749a06035910eab01e6cd..0dbc73efab1cbd4d98fa77d7a72= a2b665203511b 100644 --- a/net/x25/x25_in.c +++ b/net/x25/x25_in.c @@ -44,10 +44,9 @@ static int x25_queue_rx_frame(struct sock *sk, struct sk= _buff *skb, int more) if (x25->fraglen > 0) { /* End of fragment */ int len =3D x25->fraglen + skb->len; =20 - if ((skbn =3D alloc_skb(len, GFP_ATOMIC)) =3D=3D NULL){ - kfree_skb(skb); + skbn =3D alloc_skb(len, GFP_ATOMIC); + if (!skbn) return 1; - } =20 skb_queue_tail(&x25->fragment_queue, skb); =20 --=20 2.47.3