From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f171.google.com (mail-pl1-f171.google.com [209.85.214.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 781C8315760 for ; Tue, 23 Dec 2025 20:36:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766522183; cv=none; b=k9reWP/kyYCjAF8WowLGefhrsV1KwEKTqZNDEbckfry/1hOvxUv5lBPBhnRw2QpgpHFXk+1C4j9uPZQcddaHXtx3uef37Hc18oKxqd4gh3BXwRQJWeN4n1+nnWLW3rIZthc4IkBae8hdA5tPhZyKbHVrouOfGVOEbLBhFb3yIRk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766522183; c=relaxed/simple; bh=/Nccpglg2sCNvCsF7vVOy9nrDSxd6FnWQS59wgWVhtg=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=HJU5IN3oZ5MbTvs7WY1Y+nWlTPbEXR/3u2CYkUhakjZxqd2pgAlVkJbdO0G+0xpNiT21/ygWKK5HPfB6ir9RjIB9r0lodiSw99LVth730pRsrvvkD30cgGzhGGvdo4pFRdhE+cX/WQXK6/SwPJ8En/D6CFAcWHpf34+efPe006A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=mCNdZTx2; arc=none smtp.client-ip=209.85.214.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="mCNdZTx2" Received: by mail-pl1-f171.google.com with SMTP id d9443c01a7336-2a0d5c365ceso67720295ad.3 for ; Tue, 23 Dec 2025 12:36:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1766522180; x=1767126980; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=8W0pAdXDwSRhdNtMWGqkI9+0Gzu+9fko+sM3+ZxRRks=; b=mCNdZTx2ojHNEWkI1YZBFecoT0TZ+u+TvBfE+FzagYl0njXisdLIYjFv5g9tqW0U0F hR2XcJjYA9lqQMvopoiP7KZYl4RFvhsAAeFgiiVfI9mY3FdWWQzpmyEp7SER+4VwgJSl dB6GF2cyluF6DV6BFnPfmeyFnbGkjTfjKRuYKGXbAY92jYwHlAy8EJS/foNdT+heVVk9 M0wJPCetbdikz2cCyN0yC8Iik6nPtifUz52SddIIML2ExcGtAtPLReUS+8MOMU8lIIuh FDnlsuShEDIEsLyW5b4OgkRXFY5ozB6Q2JJ7VnR13vTHYteg1xg622lkVVXNUNHOhlCC 9u7g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1766522180; x=1767126980; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=8W0pAdXDwSRhdNtMWGqkI9+0Gzu+9fko+sM3+ZxRRks=; b=H8x4Z4K53EK9DSmPaXhi0JeRj+1Pz35Pq/qXo50vM2OrLsEZMxDpzjHzhpt+Vm4WWr ojB8mQxD5eNeTENcuyD9A9ilvNhOYSfcKmAmQEUesnLxVbS9FwzIyFHR/zDrTfs2JR7O b3SjSOrFwvu1wzCmaNoYpEXuJKb7oD2/EcuogpQSJgyctY+w8hcBl/PbA/Mb6+Ec7hB7 qc1sKgEWgjhXltZX99qII6eY6OJdF/m59PtqXg971TjvuqWE70Bw/LRMGzVAyWO5BJ7h ywXrVm2WKlM5TnC4Sq1Hlfz1W3QcYvEKaMZMyw6V9VF63viVit1/6lWYb0JhjLU9paBe RrzQ== X-Forwarded-Encrypted: i=1; AJvYcCUwkp+ngWFXBkeNMMYjkUfEEbsIQFOe4YRc6NR7EDaz/Vv3m7c8DdC0+ElGLI3AQ5VJ98HxrZg=@vger.kernel.org X-Gm-Message-State: AOJu0YzgFsssp3pOo9KoW+C9zeBCGLx8DXYtwqVCNdaS71+g8S02CEoh JnfeQtEDf59QVsvqC9iwuii3P6fRVHd6cuVh/fOwEHk8aLoP3bxQ42Dp X-Gm-Gg: AY/fxX5ixW3LHNHM2lbZMhYz/CpiR8COH+4olcsxU+vaLUyOmC6yaWBbZNSDlufXlMN HfeJlOQSw4h46Yo0zaEgH0+wZ+JO4wnSFtEEUOPDCyRQ7ePUi9jjMVDRH+swX6PITLmknNbN5UR pnWjDKlbcFSvwto7cM/qtY2o9uCC+2seZ5yGfSkpyYa/Q2oOuNzopyxWZIzhl002WXQdqriY8M6 RLuwnBjrf4vk+d/YeLVefzrYCkwLzFCWR6QkhLNjZZOATouDd2WWq1dU7ctg4WfarNC4fNekWtT 3tmspiko+5WzbKPcc/FrlEJniEVGTTjt0/nXx/rR4o+rIFr/56AQtFfU6F30jKq0J3Nw9YsLbvL w1b74wveqNFSwSLb3DAHOTVX9iwScVQSEh/ccIig2Vwsq0JhywuYkGCBpUAzXMvU66MmuSip54M 7GFmQYyKHRvdUghRg9PtR0gPG5gGzgVNvoeRnIhEc= X-Google-Smtp-Source: AGHT+IEWmGBvaWT9oSau2/R/fh/7OvDd5bOP9C8tPlI4eGo18oCy4AueFhwKRM0vwQ0K6zZg/1vwXg== X-Received: by 2002:a17:902:f684:b0:2a1:3ee3:c6ae with SMTP id d9443c01a7336-2a2f293faedmr142818705ad.59.1766522179629; Tue, 23 Dec 2025 12:36:19 -0800 (PST) Received: from SLSGDTSWING002.tail0ac356.ts.net ([129.126.109.177]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a2f3d4cb25sm137245175ad.56.2025.12.23.12.36.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Dec 2025 12:36:17 -0800 (PST) From: bestswngs@gmail.com To: security@kernel.org Cc: edumazet@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, xmei5@asu.edu, Weiming Shi Subject: [PATCH net v5] net: sock: fix hardened usercopy panic in sock_recv_errqueue Date: Wed, 24 Dec 2025 04:35:35 +0800 Message-ID: <20251223203534.1392218-2-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Weiming Shi skbuff_fclone_cache was created without defining a usercopy region, [1] unlike skbuff_head_cache which properly whitelists the cb[] field. [2] This causes a usercopy BUG() when CONFIG_HARDENED_USERCOPY is enabled and the kernel attempts to copy sk_buff.cb data to userspace via sock_recv_errqueue() -> put_cmsg(). The crash occurs when: 1. TCP allocates an skb using alloc_skb_fclone() (from skbuff_fclone_cache) [1] 2. The skb is cloned via skb_clone() using the pre-allocated fclone [3] 3. The cloned skb is queued to sk_error_queue for timestamp reporting 4. Userspace reads the error queue via recvmsg(MSG_ERRQUEUE) 5. sock_recv_errqueue() calls put_cmsg() to copy serr->ee from skb->cb [4] 6. __check_heap_object() fails because skbuff_fclone_cache has no usercopy whitelist [5] When cloned skbs allocated from skbuff_fclone_cache are used in the socket error queue, accessing the sock_exterr_skb structure in skb->cb via put_cmsg() triggers a usercopy hardening violation: [ 5.379589] usercopy: Kernel memory exposure attempt detected from SLUB object 'skbuff_fclone_cache' (offset 296, size 16)! [ 5.382796] kernel BUG at mm/usercopy.c:102! [ 5.383923] Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI [ 5.384903] CPU: 1 UID: 0 PID: 138 Comm: poc_put_cmsg Not tainted 6.12.57 #7 [ 5.384903] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 5.384903] RIP: 0010:usercopy_abort+0x6c/0x80 [ 5.384903] Code: 1a 86 51 48 c7 c2 40 15 1a 86 41 52 48 c7 c7 c0 15 1a 86 48 0f 45 d6 48 c7 c6 80 15 1a 86 48 89 c1 49 0f 45 f3 e8 84 27 88 ff <0f> 0b 490 [ 5.384903] RSP: 0018:ffffc900006f77a8 EFLAGS: 00010246 [ 5.384903] RAX: 000000000000006f RBX: ffff88800f0ad2a8 RCX: 1ffffffff0f72e74 [ 5.384903] RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffff87b973a0 [ 5.384903] RBP: 0000000000000010 R08: 0000000000000000 R09: fffffbfff0f72e74 [ 5.384903] R10: 0000000000000003 R11: 79706f6372657375 R12: 0000000000000001 [ 5.384903] R13: ffff88800f0ad2b8 R14: ffffea00003c2b40 R15: ffffea00003c2b00 [ 5.384903] FS: 0000000011bc4380(0000) GS:ffff8880bf100000(0000) knlGS:0000000000000000 [ 5.384903] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 5.384903] CR2: 000056aa3b8e5fe4 CR3: 000000000ea26004 CR4: 0000000000770ef0 [ 5.384903] PKRU: 55555554 [ 5.384903] Call Trace: [ 5.384903] [ 5.384903] __check_heap_object+0x9a/0xd0 [ 5.384903] __check_object_size+0x46c/0x690 [ 5.384903] put_cmsg+0x129/0x5e0 [ 5.384903] sock_recv_errqueue+0x22f/0x380 [ 5.384903] tls_sw_recvmsg+0x7ed/0x1960 [ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5 [ 5.384903] ? schedule+0x6d/0x270 [ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5 [ 5.384903] ? mutex_unlock+0x81/0xd0 [ 5.384903] ? __pfx_mutex_unlock+0x10/0x10 [ 5.384903] ? __pfx_tls_sw_recvmsg+0x10/0x10 [ 5.384903] ? _raw_spin_lock_irqsave+0x8f/0xf0 [ 5.384903] ? _raw_read_unlock_irqrestore+0x20/0x40 [ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5 The crash offset 296 corresponds to skb2->cb within skbuff_fclones: - sizeof(struct sk_buff) = 232 - offsetof(struct sk_buff, cb) = 40 - offset of skb2.cb in fclones = 232 + 40 = 272 - crash offset 296 = 272 + 24 (inside sock_exterr_skb.ee) This patch uses a local stack variable as a bounce buffer to avoid the hardened usercopy check failure. [1] https://elixir.bootlin.com/linux/v6.12.62/source/net/ipv4/tcp.c#L885 [2] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5104 [3] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5566 [4] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5491 [5] https://elixir.bootlin.com/linux/v6.12.62/source/mm/slub.c#L5719 Fixes: 6d07d1cd300f ("usercopy: Restrict non-usercopy caches to size 0") Reported-by: Xiang Mei Signed-off-by: Weiming Shi --- v2: Fix the Commit Message v3: Add "From" email address, Fix "CC" and "TO" email address v4: Fix The Patch Code v5: Use a bounce buffer for copying skb->mark net/core/sock.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/net/core/sock.c b/net/core/sock.c index 45c98bf524b2..a1c8b47b0d56 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -3896,7 +3896,7 @@ void sock_enable_timestamp(struct sock *sk, enum sock_flags flag) int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len, int level, int type) { - struct sock_exterr_skb *serr; + struct sock_extended_err ee; struct sk_buff *skb; int copied, err; @@ -3916,8 +3916,9 @@ int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len, sock_recv_timestamp(msg, sk, skb); - serr = SKB_EXT_ERR(skb); - put_cmsg(msg, level, type, sizeof(serr->ee), &serr->ee); + /* We must use a bounce buffer for CONFIG_HARDENED_USERCOPY=y */ + ee = SKB_EXT_ERR(skb)->ee; + put_cmsg(msg, level, type, sizeof(ee), &ee); msg->msg_flags |= MSG_ERRQUEUE; err = copied; -- 2.43.0