From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2589C29B78F for ; Thu, 4 Jun 2026 10:30:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780569041; cv=none; b=KEqyEYNSRrXeL5hOlUIDFTFv4BtDY1I6BO7BmAz9fZ9ILn/HfqrOIDzb2wMbzx2hQFIrvX2FsR8O7x5sNt1zTsbdy4WikXE9L197HlyK2SSPexsR1RNmhnhMOinvqYTcELvOP2mEQjCO91XpBQP3aHztK5MgMUyeHBA0k7DWcBY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780569041; c=relaxed/simple; bh=oLqV6/EmOuNtZ1uAPTPiPDCIE/maBC+zMkSEN6W6Gnw=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=OkvehLjhBKLuNpcgSatycIfL2lerc6GF9YZWUXcidWtqlOJMP1Fagr4MVBWXuFZrfGQS74zm4smIT9aDj0v09hYxiKR+HfkbmN7wOoHca/HcHTovd8b9tnHHos3oQpXKkJNaVKpNP4+cTlQGOINmPebykmLK9D39NAqGnSGvakU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=i2f+Ctuu; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="i2f+Ctuu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0FC241F00893; Thu, 4 Jun 2026 10:30:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780569039; bh=EhkxAz1RP05ncqi18M4zNYUB8xOSS7qw4iabtNJQpQA=; h=Subject:To:Cc:From:Date; b=i2f+Ctuu0jKr9zaRb1q3wsbgQe9a1engFzqu0QTkKJSNPmUQ5RpbtwBqqj5a22bJ8 H0gTHuuNYIEL3MLQFxGPxinJBPv2yexwPAfyuqfnF5uaOC9F9KNKkDIjYYqLsUDs3I fCl7GPDymcgeFWhY7v+BXJeXcwEKGUKZH6q0rFAg= Subject: FAILED: patch "[PATCH] net: skbuff: fix missing zerocopy reference in pskb_carve" failed to apply to 6.1-stable tree To: minhnguyen.080505@gmail.com,pabeni@redhat.com,willemb@google.com Cc: From: Date: Thu, 04 Jun 2026 12:29:40 +0200 Message-ID: <2026060440-cinch-zone-22b5@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 98d0912e9f841e5529a5b89a972805f34cb1c69d # git commit -s git send-email --to '' --in-reply-to '2026060440-cinch-zone-22b5@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 98d0912e9f841e5529a5b89a972805f34cb1c69d Mon Sep 17 00:00:00 2001 From: Minh Nguyen Date: Tue, 26 May 2026 11:12:39 +0700 Subject: [PATCH] net: skbuff: fix missing zerocopy reference in pskb_carve helpers pskb_carve_inside_header() and pskb_carve_inside_nonlinear() both copy the old skb_shared_info header into a new buffer via memcpy(), which includes the destructor_arg pointer (uarg) for MSG_ZEROCOPY skbs. Neither function calls net_zcopy_get() for the new shinfo, creating an unaccounted holder: every skb_shared_info with destructor_arg set will call skb_zcopy_clear() once when freed, but the corresponding net_zcopy_get() was never called for the new copy. Repeated calls drive uarg->refcnt to zero prematurely, freeing ubuf_info_msgzc while TX skbs still hold live destructor_arg pointers. KASAN reports use-after-free on a freed ubuf_info_msgzc: BUG: KASAN: slab-use-after-free in skb_release_data+0x77b/0x810 Read of size 8 at addr ffff88801574d3e8 by task poc/220 Call Trace: skb_release_data+0x77b/0x810 kfree_skb_list_reason+0x13e/0x610 skb_release_data+0x4cd/0x810 sk_skb_reason_drop+0xf3/0x340 skb_queue_purge_reason+0x282/0x440 rds_tcp_inc_free+0x1e/0x30 rds_recvmsg+0x354/0x1780 __sys_recvmsg+0xdf/0x180 Allocated by task 219: msg_zerocopy_realloc+0x157/0x7b0 tcp_sendmsg_locked+0x2892/0x3ba0 Freed by task 219: ip_recv_error+0x74a/0xb10 tcp_recvmsg+0x475/0x530 The skb consuming the late access still referenced the same uarg via shinfo->destructor_arg copied by pskb_carve_inside_nonlinear() without a refcount bump. This has been verified to be reliably exploitable: a working proof-of-concept achieves full root privilege escalation from an unprivileged local user on a default kernel configuration. The fix follows the pattern of pskb_expand_head() which has the same memcpy/cloned structure. For pskb_carve_inside_header(), net_zcopy_get() is placed after skb_orphan_frags() succeeds, so the orphan error path needs no cleanup. For pskb_carve_inside_nonlinear(), net_zcopy_get() is placed after all failure points and just before skb_release_data(), so no error path needs cleanup at all -- matching pskb_expand_head() more closely and avoiding the need for a balancing net_zcopy_put(). Fixes: 6fa01ccd8830 ("skbuff: Add pskb_extract() helper function") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-sonnet-4-6 Signed-off-by: Minh Nguyen Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260526041240.329462-1-minhnguyen.080505@gmail.com Signed-off-by: Paolo Abeni diff --git a/net/core/skbuff.c b/net/core/skbuff.c index d247acd447e4..0d3cc115f2e7 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6833,6 +6833,8 @@ static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off, skb_kfree_head(data); return -ENOMEM; } + if (skb_zcopy(skb)) + net_zcopy_get(skb_zcopy(skb)); for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) skb_frag_ref(skb, i); if (skb_has_frag_list(skb)) @@ -6976,6 +6978,8 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off, skb_kfree_head(data); return -ENOMEM; } + if (skb_zcopy(skb)) + net_zcopy_get(skb_zcopy(skb)); skb_release_data(skb, SKB_CONSUMED); skb->head = data;