From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794590203; b=a7jAVfFDS96rkuJaI1D5c7Ee2cdTecvzzmYhXfsMkToD14gupYwYSYaS+w1+EaSxOm+c OQu/xtDIVUfgHJdEsFQ8+3p89f4XRYabIe1jp1sxJqhIX1nQLimlhtaJGysEPCVkkRnEB NJu6KmrMGOVw79I7reB9T2oCH7RJ4Og1z2SLLU/9Gbgq6SmWhYTEkE6hshUc+Jk2Aaz1b pn7eChiw8J+B+9S74sskro02UdJ7Bw7Hn55sJTC3I45y5C5mO01db1qI/Orsz/pH5ilAf 0dbNgoQFkj4UWVEDs7/sSCek9ySBWbfG63hFDbGoRTIXcKE3Oq7W/A4zy9ZfE16+V4Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590203; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=swiWuXHW9wDOJu1TLMO6Ypsu5TH3YwDFvUDBiMmOBLc=; b=2M5S8sP1CQAEznWKSChr0HnbG836VEL74z1UDDUZgZ3BOtpv84jmLdPnW8wlCnwmgF9P eJ89JSP9HLjqkUxg1tGXmofDuk2t30QvUe5jvx+Z5UAnbNM7BAsIcqHgWwqDZ8LxdYP0F 3+ooq27JaVyfEZleny4BXXKFS3BJbnKSlNWTsNGM9hmxQ2qbJHRj0hCiA+j7UhBWB2uEX 89pe13ok/zvZy8LsmAbSv/82Abo4JJb6S+wRlt9E6j+TNwIZ3Ke566awmw9GNiDj6tgC/ J5hFJXn8xNsVHPtDoAHdzkkJrZ1DwVo7hL2I+113y6O3GSdeSqUC3klIAHVoOEiaHtw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b="ayIvj/g2"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 793CA606B378; Fri, 13 Nov 2026 17:16:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=ayIvj/g2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2649F1F000C7; Fri, 13 Nov 2026 17:16:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590203; bh=swiWuXHW9wDOJu1TLMO6Ypsu5TH3YwDFvUDBiMmOBLc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ayIvj/g2EazCRfsZCbFJMRIRY21x3HQHij15h+V+JBGsbkdMVfXL+gS1PU+HeTWyI 5mk5EwtSoobPMz8HbzUJvY3ibhikB2ymGMRQIzMmFrsWq5DUSSskcbViLlHp+F6zP+ GYcBPP+9r9m0IND5b8jft7xURMdt3ZlUyqktSngI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yehyeong Lee , Juergen Gross , Dominique Martinet , Sasha Levin Subject: [PATCH 6.18 208/686] 9p/xen: validate the response size from the backend Date: Fri, 13 Nov 2026 10:45:41 -0500 Message-ID: <20261113153828.083386223@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153820.902362109@linuxfoundation.org> References: <20261113153820.902362109@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yehyeong Lee [ Upstream commit 9b4cf60c6b739461c5b4ec9c52587da6b2608786 ] p9_xen_response() takes the length of an incoming response from the ring -- the first field of the 9p header, which the Xen transport reuses as its framing header -- and uses it to advance the consumer index, but never checks that it is at least the header size or no larger than the number of bytes the backend has actually produced. A malicious or buggy backend can post a response whose size is smaller than the header (for example 0). The consumer index then never advances, so the response work re-reads the same ring contents instead of making progress. In testing this raced with the teardown that the malformed reply triggers and dereferenced a freed p9_client: 9pfs 9pfs-0: Wrong req tag=ffff BUG: kernel NULL pointer dereference, address: 0000000000000060 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted 7.2.0-rc5 #6 PREEMPT(lazy) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 Workqueue: events p9_xen_response RIP: 0010:idr_find+0x4/0x10 RSP: 0018:ffffbf5d80063de8 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffffa229c21195a0 RCX: ffffa229c2400000 RDX: ffffa229c11c2200 RSI: 000000000000ffff RDI: 0000000000000050 RBP: 000000000000ffff R08: 3fffffffffffdfff R09: ffffffffffffffff R10: 3fffffffffffdfff R11: ffffffff87a60e80 R12: 0000000000000050 R13: 0000000000000000 R14: 000000000000ffff R15: 0000000000100000 FS: 0000000000000000(0000) GS:ffffa22a7661c000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000060 CR3: 000000003ac34002 CR4: 0000000000770ef0 PKRU: 55555554 Call Trace: p9_tag_lookup+0x2b/0x90 p9_xen_response+0x17c/0x2e0 process_one_work+0x16a/0x3a0 worker_thread+0x172/0x2e0 kthread+0xdd/0x110 ret_from_fork+0x18b/0x240 ret_from_fork_asm+0x1a/0x30 Modules linked in: CR2: 0000000000000060 ---[ end trace 0000000000000000 ]--- Reject a response whose size is outside [sizeof(header), queued] before using it, matching the validation the backend already applies to incoming requests. Fixes: f66c72bea129 ("xen/9pfs: receive responses") Cc: stable@vger.kernel.org Signed-off-by: Yehyeong Lee Reviewed-by: Juergen Gross Message-ID: <20261005125640.274054-1-yhlee@isslab.korea.ac.kr> Signed-off-by: Dominique Martinet Signed-off-by: Sasha Levin --- net/9p/trans_xen.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c index 92701a16511d4..67f464acf6171 100644 --- a/net/9p/trans_xen.c +++ b/net/9p/trans_xen.c @@ -198,6 +198,14 @@ static void p9_xen_response(struct work_struct *work) masked_prod, &masked_cons, XEN_9PFS_RING_SIZE(ring)); + if (h.size < sizeof(h) || + h.size > xen_9pfs_queued(prod, cons, + XEN_9PFS_RING_SIZE(ring))) { + dev_warn_ratelimited(&priv->dev->dev, + "bad response size %u from backend\n", h.size); + break; + } + req = p9_tag_lookup(priv->client, h.tag); if (!req || req->status != REQ_STATUS_SENT) { dev_warn(&priv->dev->dev, "Wrong req tag=%x\n", h.tag); -- 2.53.0