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 378DD40E8D4 for ; Fri, 5 Jun 2026 13:57:41 +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=1780667862; cv=none; b=rLqGvYvbaV4ZcQpNE9H9yRNcLtIRnyv6hWVew8pfrX+us6THr7ovmTrBSWLQTuU6N+Z5ZfUTsj5VmjrF52LfMHiWIW6W91NIyt7VII3lvrp5I5WSLk/JjF/5AEHYDlqJWKjfUuuINxPlw99qDkanN7V+T0GV0dvy4P37HbV+tMc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780667862; c=relaxed/simple; bh=taH/htxfRp9G4UgPJtZqDtvorB6jBmbIMN5saL8XvvA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tYwEAeeGXN95GjSS9B0fEUw2GgetVIzg5ESAUGstZSZmaWJ1P7n40mBc7X0ywmd7PBuRSkxIW1lzr8X6HKGck/i+19ou/SnYow8ObRNoPBh3Qf9hTxJ6if7YKzi2AcsAGV6D9HGrDZIIOk3TxwTNDps8d0C4gdeP7hl+cGN+6sk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GkxuCf4J; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GkxuCf4J" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A6351F00893; Fri, 5 Jun 2026 13:57:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780667860; bh=p+pDPyuSe1H0YRTE0CLkxO2+TZksjNBHbrdDj6NRH68=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=GkxuCf4JdpHqEKMEGIAISZdbUuXAnEqcMgrhdZqRPUR5cm+aNLbgs2Ws94O5TJoYM 5+uOqaDbf4bLFjmcrBwKiLCdlSK7RhzF5zLw5kve1y3obrAZPHvg0owg5uFfVKtUQd 9omyft1Swkyev5EsABeyAJbjvZNlGNhcRmrBJKrgxw+kXhckW5lII0cbOso48KEV1P pf9bCE5F9N9Ldg4fojk7/aC4aaU/SZnRmc1PmQ/5RzhiRptm3CETFTGQWNUre1g+4y eXiJaui38/6i9VW7rKqzFqINpMosNToUnI666yAPrQq7vvVRDaN/Fq7e1kB2bVLj0j cn/rphMhBlsQA== From: Sasha Levin To: stable@vger.kernel.org Cc: Minh Nguyen , Willem de Bruijn , Paolo Abeni , Sasha Levin Subject: [PATCH 5.15.y] net: skbuff: fix missing zerocopy reference in pskb_carve helpers Date: Fri, 5 Jun 2026 09:57:38 -0400 Message-ID: <20260605135738.973875-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026060441-bullfrog-dealer-0f27@gregkh> References: <2026060441-bullfrog-dealer-0f27@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Minh Nguyen [ Upstream commit 98d0912e9f841e5529a5b89a972805f34cb1c69d ] 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: Sasha Levin --- net/core/skbuff.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index a8d09eff26f11c..d363d2f6f576c1 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6256,6 +6256,8 @@ static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off, kfree(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)) @@ -6404,6 +6406,8 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off, kfree(data); return -ENOMEM; } + if (skb_zcopy(skb)) + net_zcopy_get(skb_zcopy(skb)); skb_release_data(skb); skb->head = data; -- 2.53.0