netdev - [PATCH] net: sched: Annotate struct tc_pedit with __counted

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Date: Fri, 16 Feb 2024 15:27:44 -0800
From: Kees Cook <keescook@...omium.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	netdev@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] net: sched: Annotate struct tc_pedit with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct tc_pedit.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Jiri Pirko <jiri@...nulli.us>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: netdev@...r.kernel.org
Cc: linux-hardening@...r.kernel.org
---
 include/uapi/linux/tc_act/tc_pedit.h | 2 +-
 net/sched/act_pedit.c                | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/tc_act/tc_pedit.h b/include/uapi/linux/tc_act/tc_pedit.h
index f3e61b04fa01..f5cab7fc96ab 100644
--- a/include/uapi/linux/tc_act/tc_pedit.h
+++ b/include/uapi/linux/tc_act/tc_pedit.h
@@ -62,7 +62,7 @@ struct tc_pedit_sel {
 	tc_gen;
 	unsigned char           nkeys;
 	unsigned char           flags;
-	struct tc_pedit_key     keys[0];
+	struct tc_pedit_key     keys[] __counted_by(nkeys);
 };
 
 #define tc_pedit tc_pedit_sel
diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
index 2ef22969f274..21e863d2898c 100644
--- a/net/sched/act_pedit.c
+++ b/net/sched/act_pedit.c
@@ -515,11 +515,11 @@ static int tcf_pedit_dump(struct sk_buff *skb, struct tc_action *a,
 		spin_unlock_bh(&p->tcf_lock);
 		return -ENOBUFS;
 	}
+	opt->nkeys = parms->tcfp_nkeys;
 
 	memcpy(opt->keys, parms->tcfp_keys,
 	       flex_array_size(opt, keys, parms->tcfp_nkeys));
 	opt->index = p->tcf_index;
-	opt->nkeys = parms->tcfp_nkeys;
 	opt->flags = parms->tcfp_flags;
 	opt->action = p->tcf_action;
 	opt->refcnt = refcount_read(&p->tcf_refcnt) - ref;
-- 
2.34.1