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 <[email protected]>

---
Cc: Jakub Kicinski <[email protected]>
Cc: Jamal Hadi Salim <[email protected]>
Cc: Cong Wang <[email protected]>
Cc: Jiri Pirko <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: [email protected]
Cc: [email protected]

---
  include/uapi/linux/tc_act/tc_pedit.h | 2 +-
  net/sched/act_pedit.c                | 2 +-
  2 files changed, 2 insertions(+), 2 deletions(-)

include/uapi/linux/tc_act/tc_pedit.h +1 -1

index f3e61b04fa01..f5cab7fc96ab 100644
@@ -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

net/sched/act_pedit.c +1 -1

index 2ef22969f274..21e863d2898c 100644
@@ -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;

Quoted 12 lines · Kees Cook

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 <[email protected]>

Quoted 11 lines

---
Cc: Jakub Kicinski <[email protected]>
Cc: Jamal Hadi Salim <[email protected]>
Cc: Cong Wang <[email protected]>
Cc: Jiri Pirko <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: [email protected]
Cc: [email protected]

opt->nkeys updated before memcpy(), looks good to me:

Reviewed-by Gustavo A. R. Silva <[email protected]>

Thanks!
--
Gustavo

Quoted 35 lines

---
  include/uapi/linux/tc_act/tc_pedit.h | 2 +-
  net/sched/act_pedit.c                | 2 +-
  2 files changed, 2 insertions(+), 2 deletions(-)

include/uapi/linux/tc_act/tc_pedit.h +1 -1

index f3e61b04fa01..f5cab7fc96ab 100644
@@ -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

net/sched/act_pedit.c +1 -1

index 2ef22969f274..21e863d2898c 100644
@@ -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;