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 1385D2FB97B; Sun, 7 Jun 2026 10:44:40 +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=1780829081; cv=none; b=bRBs7mQW8vW3q2ukKtN/q/Jx7eJR/6Vk+8ygrDITXrtvQV25R8jGzrAkRfGE5AfXWz4X2vNV17AHPMh7QTv0NIR0g+nfodBosuy5ITvEvSL1/R0K7/sdl2HQH7DeXhFlVH69IkdM7dyLmM/q6NhUuXntKLPGaF+KQ6mzgtup8cs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780829081; c=relaxed/simple; bh=VrUERb7WaI2+0ZXcokcq0gjANM6VIT1hsWABI+uDcoY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CHrBPWWYVaX19KRWb4JWY36Ow+HfJHvOKLgP0Nx04zO8QouON23FOjBCiPUi2mz0BguSk/2eENfVYcO4BF1wJ3TxopsNBEq1XWR4koPanO9JggH6plcEbgGydlPSsooEvH8kkQquK6Y5513WCAl5NBhPVhnRRe+Vq8QjnnZExhA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=MLisGMZ3; 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="MLisGMZ3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE74B1F00893; Sun, 7 Jun 2026 10:44:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780829080; bh=w5Uz6RUiPGtB02XQ9AS13YmqjUtVndUosOA7tC9pvbU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=MLisGMZ3PjewlfL/X85YudqVEMaarT0viDxht8mBHTpQ8CSVZ1D7HIR16ZmgaSNrV oCDnZ6eQBdPsZjkXJ7wEniKKoGyccNds6odij4wQZL36BcShN2sGpK+7wfPtvX6jCT G+c/e5Jt1w+KpM+93aA4QfGzxQwPcdlpFaszvCNE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Minh Nguyen , Willem de Bruijn , Paolo Abeni Subject: [PATCH 6.12 194/307] net: skbuff: fix missing zerocopy reference in pskb_carve helpers Date: Sun, 7 Jun 2026 11:59:51 +0200 Message-ID: <20260607095734.850931791@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260607095727.647295505@linuxfoundation.org> References: <20260607095727.647295505@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Minh Nguyen commit 98d0912e9f841e5529a5b89a972805f34cb1c69d upstream. 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 Signed-off-by: Greg Kroah-Hartman --- net/core/skbuff.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6704,6 +6704,8 @@ static int pskb_carve_inside_header(stru skb_kfree_head(data, size); 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)) @@ -6853,6 +6855,8 @@ static int pskb_carve_inside_nonlinear(s skb_kfree_head(data, size); return -ENOMEM; } + if (skb_zcopy(skb)) + net_zcopy_get(skb_zcopy(skb)); skb_release_data(skb, SKB_CONSUMED); skb->head = data;