From: Xiang Mei Date: Tue, 31 Mar 2026 05:02:15 +0000 (-0700) Subject: net/sched: cls_fw: fix NULL pointer dereference on shared blocks X-Git-Tag: v7.0-rc7~28^2~6 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=faeea8bbf6e958bf3c00cb08263109661975987c;p=thirdparty%2Fkernel%2Fstable.git net/sched: cls_fw: fix NULL pointer dereference on shared blocks The old-method path in fw_classify() calls tcf_block_q() and dereferences q->handle. Shared blocks leave block->q NULL, causing a NULL deref when an empty cls_fw filter is attached to a shared block and a packet with a nonzero major skb mark is classified. Reject the configuration in fw_change() when the old method (no TCA_OPTIONS) is used on a shared block, since fw_classify()'s old-method path needs block->q which is NULL for shared blocks. The fixed null-ptr-deref calling stack: KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:fw_classify (net/sched/cls_fw.c:81) Call Trace: tcf_classify (./include/net/tc_wrapper.h:197 net/sched/cls_api.c:1764 net/sched/cls_api.c:1860) tc_run (net/core/dev.c:4401) __dev_queue_xmit (net/core/dev.c:4535 net/core/dev.c:4790) Fixes: 1abf272022cf ("net: sched: tcindex, fw, flow: use tcf_block_q helper to get struct Qdisc") Reported-by: Weiming Shi Signed-off-by: Xiang Mei Acked-by: Jamal Hadi Salim Link: https://patch.msgid.link/20260331050217.504278-1-xmei5@asu.edu Signed-off-by: Paolo Abeni --- diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c index be81c108179d..23884ef8b80c 100644 --- a/net/sched/cls_fw.c +++ b/net/sched/cls_fw.c @@ -247,8 +247,18 @@ static int fw_change(struct net *net, struct sk_buff *in_skb, struct nlattr *tb[TCA_FW_MAX + 1]; int err; - if (!opt) - return handle ? -EINVAL : 0; /* Succeed if it is old method. */ + if (!opt) { + if (handle) + return -EINVAL; + + if (tcf_block_shared(tp->chain->block)) { + NL_SET_ERR_MSG(extack, + "Must specify mark when attaching fw filter to block"); + return -EINVAL; + } + + return 0; /* Succeed if it is old method. */ + } err = nla_parse_nested_deprecated(tb, TCA_FW_MAX, opt, fw_policy, NULL);