From nobody Wed Feb 11 07:48:30 2026 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 0478221A434; Sat, 10 Jan 2026 08:07:25 +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=1768032446; cv=none; b=WnVptZ1+ijMz34TNXs+zbdD23AQ8R4Aw/FMQTQ8gjLOYStjEV66ZlAF6BSHvU+HznwttloKAfy50RJWlunLuH+0+zIVOyEoW7kcl88uN2yYPxh1vpWKmWRmcbtUD8GrzXGh6fZArS7GjR2SkC88Mmwhqm/Tuvjv/R6ZFTXoV6MQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768032446; c=relaxed/simple; bh=AwPIq0Wza+Ceg8Z80rRSSkUlWG5Kc4uDAuGiYngcc3M=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=ebuhtC8SxDgdMsb5UINAeVzEDRaW90dU3rwLJzeJsgbDEZrPGtkZVQmg9TGcjzxu8SWZthwTZcGMhm/uj/XYIwkl/UlhuFKVw1l8IJtppptS/sV4Dm9YkELSRDHbEpmU0syq3rq11PT2dwpyGK80bfMk2eH2W/cj9CqBlWI71I0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=f+/Jm+MC; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="f+/Jm+MC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 80898C4CEF1; Sat, 10 Jan 2026 08:07:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768032445; bh=AwPIq0Wza+Ceg8Z80rRSSkUlWG5Kc4uDAuGiYngcc3M=; h=Date:From:To:Cc:Subject:From; b=f+/Jm+MCs+sTcBRSN9lnwRJ5PbjQTbAmDTWPlpwallGeJSUR2Nc2s+JmRFYouhaZW +UnfXg9rNBNdNmJTP4rfIw9EYlfZsL1Fuq4j94u9ozP1YIpJxtsKsoMyFsMwLs23P7 DP9xb420UCl+08ivStzeBfwrVEkPb7R2ZuzSKTFaxoafou4nVBaw3zmVC03cikyiJE qndMRiEgeo/Enyp5qEURBKvEJzfZoj+tydEDXAMj+g8zrgElnO75gWZi01PP8hAQe2 Trqeb+C5ld/TL5OV4a+R4GqO/CEYm0C9HAQphnVjrP57xyDNhNFOEQWAonhhsWiHgD 7W3QaUsRk3siw== Date: Sat, 10 Jan 2026 17:07:17 +0900 From: "Gustavo A. R. Silva" To: "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Akihiko Odaki , Simon Horman Cc: netdev@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org, Kees Cook Subject: [PATCH v2][next] virtio_net: Fix misalignment bug in struct virtnet_info Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use the new TRAILING_OVERLAP() helper to fix a misalignment bug along with the following warning: drivers/net/virtio_net.c:429:46: warning: structure containing a flexible a= rray member is not at the end of another structure [-Wflex-array-member-not= -at-end] This helper creates a union between a flexible-array member (FAM) and a set of members that would otherwise follow it (in this case `u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];`). This overlays the trailing members (rss_hash_key_data) onto the FAM (hash_key_data) while keeping the FAM and the start of MEMBERS aligned. The static_assert() ensures this alignment remains. Notice that due to tail padding in flexible `struct virtio_net_rss_config_trailer`, `rss_trailer.hash_key_data` (at offset 83 in struct virtnet_info) and `rss_hash_key_data` (at offset 84 in struct virtnet_info) are misaligned by one byte. See below: struct virtio_net_rss_config_trailer { __le16 max_tx_vq; /* 0 2 */ __u8 hash_key_length; /* 2 1 */ __u8 hash_key_data[]; /* 3 0 */ /* size: 4, cachelines: 1, members: 3 */ /* padding: 1 */ /* last cacheline: 4 bytes */ }; struct virtnet_info { ... struct virtio_net_rss_config_trailer rss_trailer; /* 80 4 */ /* XXX last struct has 1 byte of padding */ u8 rss_hash_key_data[40]; /* 84 40 */ ... /* size: 832, cachelines: 13, members: 48 */ /* sum members: 801, holes: 8, sum holes: 31 */ /* paddings: 2, sum paddings: 5 */ }; After changes, those members are correctly aligned at offset 795: struct virtnet_info { ... union { struct virtio_net_rss_config_trailer rss_trailer; /* 792 = 4 */ struct { unsigned char __offset_to_hash_key_data[3]; /* 79= 2 3 */ u8 rss_hash_key_data[40]; /* 795 40 */ }; /* 792 43 */ }; /* 792 44 */ ... /* size: 840, cachelines: 14, members: 47 */ /* sum members: 801, holes: 8, sum holes: 35 */ /* padding: 4 */ /* paddings: 1, sum paddings: 4 */ /* last cacheline: 8 bytes */ }; As a result, the RSS key passed to the device is shifted by 1 byte: the last byte is cut off, and instead a (possibly uninitialized) byte is added at the beginning. As a last note `struct virtio_net_rss_config_hdr *rss_hdr;` is also moved to the end, since it seems those three members should stick around together. :) Cc: stable@vger.kernel.org Fixes: ed3100e90d0d ("virtio_net: Use new RSS config structs") Signed-off-by: Gustavo A. R. Silva Acked-by: Michael S. Tsirkin --- Changes in v2: - Update subject and changelog text (include feedback from Simon and Michael --thanks folks) - Add Fixes tag and CC -stable. v1: - Link: https://lore.kernel.org/linux-hardening/aLiYrQGdGmaDTtLF@kspp/ drivers/net/virtio_net.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 22d894101c01..5cbcc9926a23 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -425,9 +425,6 @@ struct virtnet_info { u16 rss_indir_table_size; u32 rss_hash_types_supported; u32 rss_hash_types_saved; - struct virtio_net_rss_config_hdr *rss_hdr; - struct virtio_net_rss_config_trailer rss_trailer; - u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE]; =20 /* Has control virtqueue */ bool has_cvq; @@ -493,7 +490,16 @@ struct virtnet_info { struct failover *failover; =20 u64 device_stats_cap; + + struct virtio_net_rss_config_hdr *rss_hdr; + + /* Must be last as it ends in a flexible-array member. */ + TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer, hash_= key_data, + u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE]; + ); }; +static_assert(offsetof(struct virtnet_info, rss_trailer.hash_key_data) =3D= =3D + offsetof(struct virtnet_info, rss_hash_key_data)); =20 struct padded_vnet_hdr { struct virtio_net_hdr_v1_hash hdr; --=20 2.43.0