[PATCH] GPRS: Fix the byte ordering of the PDP context status IE

[Harald Welte]

It seems that 24.008 Section 10.5.7.1 specifies the IE to be encoded in
little endian...
---
 openbsc/src/gprs/gprs_gmm.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/openbsc/src/gprs/gprs_gmm.c b/openbsc/src/gprs/gprs_gmm.c
index 098e4c2..f83219f 100644
--- a/openbsc/src/gprs/gprs_gmm.c
+++ b/openbsc/src/gprs/gprs_gmm.c
@@ -870,6 +870,7 @@ static void process_ms_ctx_status(struct sgsn_mm_ctx *mmctx,
 				  uint16_t pdp_status)
 {
 	struct sgsn_pdp_ctx *pdp, *pdp2;
+	uint16_t pdp_status_reordered;
 	/* 24.008 4.7.5.1.3: If the PDP context status information element is
 	 * included in ROUTING AREA UPDATE REQUEST message, then the network
 	 * shall deactivate all those PDP contexts locally (without peer to
@@ -877,8 +878,13 @@ static void process_ms_ctx_status(struct sgsn_mm_ctx *mmctx,
 	 * state PDP-INACTIVE on network side but are indicated by the MS as
 	 * being in state PDP-INACTIVE. */
 
+	/* 24.008 10.5.7.1 indicates that the byte ordering is in fact
+	 * little endian, i.e. the first octet contains NSAPI0..7 and
+	 * the second payload octet NSAPI8..15 */
+	pdp_status_reordered = (pdp_status & 0xff << 8) || (pdp_status >> 8);
+
 	llist_for_each_entry_safe(pdp, pdp2, &mmctx->pdp_list, list) {
-		if (!(pdp_status & (1 << pdp->nsapi))) {
+		if (!(pdp_status_reordered & (1 << pdp->nsapi))) {
 			LOGP(DMM, LOGL_NOTICE, "Dropping PDP context for NSAPI=%u "
 				"due to PDP CTX STATUS IE= 0x%04x\n",
 				pdp->nsapi, pdp_status);
@@ -977,6 +983,10 @@ static int gsm48_rx_gmm_ra_upd_req(struct sgsn_mm_ctx *mmctx, struct msgb *msg,
 	if (TLVP_PRESENT(&tp, GSM48_IE_GMM_PDP_CTX_STATUS)) {
 		uint16_t pdp_status = ntohs(*(uint16_t *)
 				TLVP_VAL(&tp, GSM48_IE_GMM_PDP_CTX_STATUS));
+		/* pdp_status is now in big endian, which is the wrong
+		 * order. the wire encoding is little endian! We cannot
+		 * simply drop the ntohs() above, as we migh be running
+		 * on a big endian machine. */
 		process_ms_ctx_status(mmctx, pdp_status);
 	}
 
-- 
1.7.5.4


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