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 D8D4036C5BF; Wed, 21 Jan 2026 18:25:30 +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=1769019931; cv=none; b=IVNN4kyNdkUwBYi0tcAvnYjxOSpOx3tIVNA+hXP9j63PlH+50uUMJ3AiYi58Fx7GAcIf8l3tHyuyDSar3vDy5k2qiJkx10AFn7lBBc4rpjJ95IHtmP60sl/UtqaBpDBXbUbWUnoLD77lID9Gto+KtgoZif+dhljVdUzGvxH3jCs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769019931; c=relaxed/simple; bh=ylB4RmkQ1w+ZrdaEz8lJyZzdjq7MSNcKn0E57m+vV24=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kfCasNKKf3aFYw/a3pVXzK7oo4WE7XGONvTyLCwD6Cd920vCquSDvnOKGgC6rcsnp1BpoxNumV8ZBB7Y5QsUxVHDZtuxHmkHI4kIxNM8oQR8PNmJ9slsMoJ4J6kpUDOTeQjBHHkNZO+h/uKF9YW6ACGMUU6hUxOLvxf+rcEhrBA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=j88nWIBs; 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="j88nWIBs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 51CFEC4CEF1; Wed, 21 Jan 2026 18:25:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1769019930; bh=ylB4RmkQ1w+ZrdaEz8lJyZzdjq7MSNcKn0E57m+vV24=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=j88nWIBse0X9o6YMN4Nusa4XbI7tPnMhkUU5/VupGvcrTXYdm+0/FP1ZauIEMKfdJ J7W9M/O9Yfp0lcBDCHTs6fk4GZ/o0i3TMPvhSc1hOybpvRY3KY8B9naShLAwlejnfg ylSj47aUN8SFZm/pMuJXYd8J0DjC8kQNW9LnbYRc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Gustavo A. R. Silva" , "Michael S. Tsirkin" , Paolo Abeni Subject: [PATCH 6.18 010/198] virtio_net: Fix misalignment bug in struct virtnet_info Date: Wed, 21 Jan 2026 19:13:58 +0100 Message-ID: <20260121181418.917772029@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260121181418.537774329@linuxfoundation.org> References: <20260121181418.537774329@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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Gustavo A. R. Silva commit 4156c3745f06bc197094b9ee97a9584e69ed00bf upstream. 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 array 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]; /* 792 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 Link: https://patch.msgid.link/aWIItWq5dV9XTTCJ@kspp Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman --- drivers/net/virtio_net.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) --- 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]; /* Has control virtqueue */ bool has_cvq; @@ -493,7 +490,16 @@ struct virtnet_info { struct failover *failover; 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) == + offsetof(struct virtnet_info, rss_hash_key_data)); struct padded_vnet_hdr { struct virtio_net_hdr_v1_hash hdr;