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[72.200.102.19]) by smtp.googlemail.com with ESMTPSA id 5a478bee46e88-2b6b36550dfsm17650283eec.25.2026.01.20.07.57.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jan 2026 07:57:44 -0800 (PST) From: Will Rosenberg To: Cc: Will Rosenberg , Paul Moore , "David S. Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] cipso: harden use of skb_cow() in cipso_v4_skbuff_setattr() Date: Tue, 20 Jan 2026 08:57:38 -0700 Message-Id: <20260120155738.982771-1-whrosenb@asu.edu> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" If skb_cow() is passed a headroom <=3D -NET_SKB_PAD, it will trigger a BUG. As a result, use cases should avoid calling with a headroom that is negative to prevent triggering this issue. This is the same code pattern fixed in Commit 58fc7342b529 ("ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()"). In cipso_v4_skbuff_setattr(), len_delta can become negative, leading to a negative headroom passed to skb_cow(). However, the BUG is not triggerable because the condition headroom <=3D -NET_SKB_PAD cannot be satisfied due to limits on the IPv4 options header size. Avoid potential problems in the future by only using skb_cow() to grow the skb headroom. Signed-off-by: Will Rosenberg Acked-by: Paul Moore --- Notes: Given that IPv4 option length should not change, this may not be a worthwhile patch. =20 Apologies in advance if this ends up being a waste of time. net/ipv4/cipso_ipv4.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c index 709021197e1c..32b951ebc0c2 100644 --- a/net/ipv4/cipso_ipv4.c +++ b/net/ipv4/cipso_ipv4.c @@ -2196,7 +2196,8 @@ int cipso_v4_skbuff_setattr(struct sk_buff *skb, /* if we don't ensure enough headroom we could panic on the skb_push() * call below so make sure we have enough, we are also "mangling" the * packet so we should probably do a copy-on-write call anyway */ - ret_val =3D skb_cow(skb, skb_headroom(skb) + len_delta); + ret_val =3D skb_cow(skb, + skb_headroom(skb) + (len_delta > 0 ? len_delta : 0)); if (ret_val < 0) return ret_val; =20 base-commit: 58bae918d73e3b6cd57d1e39fcf7c75c7dd1a8fe --=20 2.34.1