Commit 7cba1833 authored by Kees Cook's avatar Kees Cook Committed by Jakub Kicinski
Browse files

net: sched: cls_u32: Avoid memcpy() false-positive warning 

To work around a misbehavior of the compiler's ability to see into
composite flexible array structs (as detailed in the coming memcpy()
hardening series[1]), use unsafe_memcpy(), as the sizing,
bounds-checking, and allocation are all very tightly coupled here.
This silences the false-positive reported by syzbot:

  memcpy: detected field-spanning write (size 80) of single field "&n->sel" at net/sched/cls_u32.c:1043 (size 16)

[1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org



Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Reported-by: default avatar <syzbot+a2c4601efc75848ba321@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/lkml/000000000000a96c0b05e97f0444@google.com/


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarJamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20220927153700.3071688-1-keescook@chromium.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 5361660a

net/sched/cls_u32.c

+5 −1
Original line number Diff line number Diff line
@@ -1040,7 +1040,11 @@ static int u32_change(struct net *net, struct sk_buff *in_skb, 
	}

#endif



	memcpy(&n->sel, s, sel_size);

	unsafe_memcpy(&n->sel, s, sel_size,

		      /* A composite flex-array structure destination,

		       * which was correctly sized with struct_size(),

		       * bounds-checked against nla_len(), and allocated

		       * above. */);

	RCU_INIT_POINTER(n->ht_up, ht);

	n->handle = handle;

	n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0;