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Tsirkin" , Jason Wang Cc: "David S. Miller" , Simon Horman , Xuan Zhuo , =?UTF-8?q?Eugenio=20P=C3=A9rez?= , Jason Xing , Kuniyuki Iwashima , =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= , Jiayuan Chen , netdev@vger.kernel.org, Alice Mikityanska Subject: [PATCH net v3 2/2] net: Guard for gso_segs overflow in skb_segment Date: Sat, 22 Aug 2026 15:01:17 +0300 Message-ID: <20260822120117.1163423-3-alice.kernel@fastmail.im> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260822120117.1163423-1-alice.kernel@fastmail.im> References: <20260822120117.1163423-1-alice.kernel@fastmail.im> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Alice Mikityanska skb_segment calculates 32-bit partial_segs as len / gso_size, and then assigns it to the 16-bit gso_segs field. The division might overflow in some edge cases where the SKB is BIG TCP (65536 <= len <= 8*65535), and gso_size < TCP_MIN_GSO_SIZE = 8. While normally this can't happen due to TCP_MIN_GSO_SIZE, an AF_PACKET PACKET_VNET_HDR socket could generate such a malformed packet until the previous patch. Blocking malformed virtio_net packets was implemented in the previous patch, but this patch clamps partial_segs in skb_segment itself for more generic robustness. Should len / gso_size happen to be bigger than 65535 in partial GSO, skb_segment will now just produce more than two output SKBs, all of which will be valid with gso_segs <= 65535. In order to catch possible other cases of too many partial_segs, add a DEBUG_NET_WARN_ON_ONCE when len / gso_size happens to be too big. Signed-off-by: Alice Mikityanska --- net/core/skbuff.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index d4382b68d56e..ceac295bb63d 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4871,7 +4871,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, * doesn't fit into an MSS sized block, so take care of that * now. */ - partial_segs = len / mss; + DEBUG_NET_WARN_ON_ONCE(len / mss > GSO_MAX_SEGS); + partial_segs = min(len / mss, GSO_MAX_SEGS); if (partial_segs > 1) mss *= partial_segs; else -- 2.55.0