From 7e0309631ecf0cd16edba72ff74747fa1b96ead3 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 1 Jan 2014 23:04:25 +0100 Subject: [PATCH] net: llc: fix order of evaluation in llc_conn_ac_inc_vr_by_1 Function llc_conn_ac_inc_vr_by_1() evaluates via macro PDU_GET_NEXT_Vr() into ... llc_sk(sk)->vR = ++llc_sk(sk)->vR & 0xffffffffffffff7f ... but the order in which the side effects take place is undefined because there is no intervening sequence point. As llc_sk(sk)->vR is written in llc_sk(sk)->vR (assignment left-hand side) and written in ++llc_sk(sk)->vR & 0xffffffffffffff7f this might possibly yield undefined behavior. The final value of llc_sk(sk)->vR is ambiguous, because, depending on the order of expression evaluation, the increment may occur before, after, or interleaved with the assignment. In C, evaluating such an expression yields undefined behavior. Since we're doing the increment via PDU_GET_NEXT_Vr() macro and the only place it is being used is from llc_conn_ac_inc_vr_by_1(), in order to increment vR by 1 with a follow-up optimized modulo, rewrite the expression into ((vR + 1) & CONST) in order to fix this. Signed-off-by: Daniel Borkmann Cc: Arnaldo Carvalho de Melo Cc: Stephen Hemminger Signed-off-by: David S. Miller --- include/net/llc_pdu.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/net/llc_pdu.h b/include/net/llc_pdu.h index 31e2de7d57c5..c0f0a13ed818 100644 --- a/include/net/llc_pdu.h +++ b/include/net/llc_pdu.h @@ -142,7 +142,7 @@ #define LLC_S_PF_IS_1(pdu) ((pdu->ctrl_2 & LLC_S_PF_BIT_MASK) ? 1 : 0) #define PDU_SUPV_GET_Nr(pdu) ((pdu->ctrl_2 & 0xFE) >> 1) -#define PDU_GET_NEXT_Vr(sn) (++sn & ~LLC_2_SEQ_NBR_MODULO) +#define PDU_GET_NEXT_Vr(sn) (((sn) + 1) & ~LLC_2_SEQ_NBR_MODULO) /* FRMR information field macros */