From: Xiang Mei Date: Tue, 31 Mar 2026 05:02:16 +0000 (-0700) Subject: net/sched: cls_flow: fix NULL pointer dereference on shared blocks X-Git-Tag: v7.0-rc7~28^2~5 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1a280dd4bd1d616a01d6ffe0de284c907b555504;p=thirdparty%2Fkernel%2Flinux.git net/sched: cls_flow: fix NULL pointer dereference on shared blocks flow_change() calls tcf_block_q() and dereferences q->handle to derive a default baseclass. Shared blocks leave block->q NULL, causing a NULL deref when a flow filter without a fully qualified baseclass is created on a shared block. Check tcf_block_shared() before accessing block->q and return -EINVAL for shared blocks. This avoids the null-deref shown below: ======================================================================= KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:flow_change (net/sched/cls_flow.c:508) Call Trace: tc_new_tfilter (net/sched/cls_api.c:2432) rtnetlink_rcv_msg (net/core/rtnetlink.c:6980) [...] ======================================================================= 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/20260331050217.504278-2-xmei5@asu.edu Signed-off-by: Paolo Abeni --- diff --git a/net/sched/cls_flow.c b/net/sched/cls_flow.c index 339c664beff6d..ab364e4e46862 100644 --- a/net/sched/cls_flow.c +++ b/net/sched/cls_flow.c @@ -503,8 +503,16 @@ static int flow_change(struct net *net, struct sk_buff *in_skb, } if (TC_H_MAJ(baseclass) == 0) { - struct Qdisc *q = tcf_block_q(tp->chain->block); + struct tcf_block *block = tp->chain->block; + struct Qdisc *q; + if (tcf_block_shared(block)) { + NL_SET_ERR_MSG(extack, + "Must specify baseclass when attaching flow filter to block"); + goto err2; + } + + q = tcf_block_q(block); baseclass = TC_H_MAKE(q->handle, baseclass); } if (TC_H_MIN(baseclass) == 0)