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6lowpan: fix off-by-one in multicast context address compression

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The second memcpy in lowpan_iphc_mcast_ctx_addr_compress() uses
&data[1] as destination and &ipaddr->s6_addr[11] as source, but
both should be offset by one: &data[2] and &ipaddr->s6_addr[12]
respectively.

This off-by-one has two consequences:
1. data[1] is overwritten with s6_addr[11], corrupting the RIID
   field in the compressed multicast address
2. data[5] is never written, so uninitialized kernel stack memory
   is transmitted over the network via lowpan_push_hc_data(),
   leaking kernel stack contents

The correct inline data layout must match what the decompression
function lowpan_uncompress_multicast_ctx_daddr() expects:
  data[0..1] = s6_addr[1..2]  (flags/scope + RIID)
  data[2..5] = s6_addr[12..15] (group ID)

Also zero-initialize the data array as a defensive measure against
similar bugs in the future.

Fixes: 5609c185f2 ("6lowpan: iphc: add support for stateful compression")
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://patch.msgid.link/20260527081806.42747-1-zhaoyz24@mails.tsinghua.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Yizhou Zhao 2026-05-27 16:18:01 +08:00 • committed by Jakub Kicinski
commit 2a58899d11
1 changed files with 2 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

4
net/6lowpan/iphc.c
View file

@ -1086,12 +1086,12 @@ static u8 lowpan_iphc_mcast_ctx_addr_compress(u8 **hc_ptr,
const struct lowpan_iphc_ctx *ctx, const struct lowpan_iphc_ctx *ctx,
const struct in6_addr *ipaddr) const struct in6_addr *ipaddr)
{ {
u8 data[6]; u8 data[6] = {};
/* flags/scope, reserved (RIID) */ /* flags/scope, reserved (RIID) */
memcpy(data, &ipaddr->s6_addr[1], 2); memcpy(data, &ipaddr->s6_addr[1], 2);
/* group ID */ /* group ID */
memcpy(&data[1], &ipaddr->s6_addr[11], 4); memcpy(&data[2], &ipaddr->s6_addr[12], 4);
lowpan_push_hc_data(hc_ptr, data, 6); lowpan_push_hc_data(hc_ptr, data, 6);
return LOWPAN_IPHC_DAM_00; return LOWPAN_IPHC_DAM_00;