[PATCH v2] monitor/rfcomm: Fix a potential memory access issue for compatibility with LLVM

[mcchou@chromium.org]

From: Miao-chen Chou <mcchou@chromium.org>

This patch replaces the use of struct rfcomm_rpn with local variables in
mmc_rpn() to prevent the access to an unaligned struct member. Since struct
rfcomm_rpn is only used in mmc_rpn(), its definition is removed. This patch
also introduces a temp variable in mcc_pn() to prevent unaligned access.
---
 monitor/rfcomm.c | 48 +++++++++++++++++++++---------------------------
 1 file changed, 21 insertions(+), 27 deletions(-)

diff --git a/monitor/rfcomm.c b/monitor/rfcomm.c
index b32ad40..6b9d355 100644
--- a/monitor/rfcomm.c
+++ b/monitor/rfcomm.c
@@ -98,16 +98,6 @@ struct rfcomm_lmsc {
 	uint8_t break_sig;
 } __attribute__((packed));

-struct rfcomm_rpn {
-	uint8_t dlci;
-	uint8_t bit_rate;
-	uint8_t parity;
-	uint8_t io;
-	uint8_t xon;
-	uint8_t xoff;
-	uint16_t pm;
-} __attribute__ ((packed));
-
 struct rfcomm_rls {
 	uint8_t dlci;
 	uint8_t error;
@@ -198,47 +188,48 @@ done:
 static inline bool mcc_rpn(struct rfcomm_frame *rfcomm_frame, uint8_t indent)
 {
 	struct l2cap_frame *frame = &rfcomm_frame->l2cap_frame;
-	struct rfcomm_rpn rpn;
+	uint8_t dlci, bit_rate, parity, io, xon, xoff;
+	uint16_t pm;

-	if (!l2cap_frame_get_u8(frame, &rpn.dlci))
+	if (!l2cap_frame_get_u8(frame, &dlci))
 		return false;

-	print_field("%*cdlci %d", indent, ' ', RFCOMM_GET_DLCI(rpn.dlci));
+	print_field("%*cdlci %d", indent, ' ', RFCOMM_GET_DLCI(dlci));

 	if (frame->size < 7)
 		goto done;

 	/* port value octets (optional) */

-	if (!l2cap_frame_get_u8(frame, &rpn.bit_rate))
+	if (!l2cap_frame_get_u8(frame, &bit_rate))
 		return false;

-	if (!l2cap_frame_get_u8(frame, &rpn.parity))
+	if (!l2cap_frame_get_u8(frame, &parity))
 		return false;

-	if (!l2cap_frame_get_u8(frame, &rpn.io))
+	if (!l2cap_frame_get_u8(frame, &io))
 		return false;

 	print_field("%*cbr %d db %d sb %d p %d pt %d xi %d xo %d", indent, ' ',
-		rpn.bit_rate, GET_RPN_DB(rpn.parity), GET_RPN_SB(rpn.parity),
-		GET_RPN_PARITY(rpn.parity), GET_RPN_PTYPE(rpn.parity),
-		GET_RPN_XIN(rpn.io), GET_RPN_XOUT(rpn.io));
+		bit_rate, GET_RPN_DB(parity), GET_RPN_SB(parity),
+		GET_RPN_PARITY(parity), GET_RPN_PTYPE(parity),
+		GET_RPN_XIN(io), GET_RPN_XOUT(io));

-	if (!l2cap_frame_get_u8(frame, &rpn.xon))
+	if (!l2cap_frame_get_u8(frame, &xon))
 		return false;

-	if (!l2cap_frame_get_u8(frame, &rpn.xoff))
+	if (!l2cap_frame_get_u8(frame, &xoff))
 		return false;

 	print_field("%*crtri %d rtro %d rtci %d rtco %d xon %d xoff %d",
-		indent, ' ', GET_RPN_RTRI(rpn.io), GET_RPN_RTRO(rpn.io),
-		GET_RPN_RTCI(rpn.io), GET_RPN_RTCO(rpn.io), rpn.xon,
-		rpn.xoff);
+		indent, ' ', GET_RPN_RTRI(io), GET_RPN_RTRO(io),
+		GET_RPN_RTCI(io), GET_RPN_RTCO(io), xon, xoff);

-	if (!l2cap_frame_get_le16(frame, &rpn.pm))
+	/* prevent unaligned memory access */
+	if (!l2cap_frame_get_le16(frame, &pm))
 		return false;

-	print_field("%*cpm 0x%04x", indent, ' ', rpn.pm);
+	print_field("%*cpm 0x%04x", indent, ' ', pm);

 done:
 	return true;
@@ -265,6 +256,7 @@ static inline bool mcc_pn(struct rfcomm_frame *rfcomm_frame, uint8_t indent)
 {
 	struct l2cap_frame *frame = &rfcomm_frame->l2cap_frame;
 	struct rfcomm_pn pn;
+	uint16_t mtu;

 	/* rfcomm_pn struct is defined in rfcomm.h */

@@ -284,8 +276,10 @@ static inline bool mcc_pn(struct rfcomm_frame *rfcomm_frame, uint8_t indent)
 	if (!l2cap_frame_get_u8(frame, &pn.ack_timer))
 		return false;

-	if (!l2cap_frame_get_le16(frame, &pn.mtu))
+	/* prevent unaligned memory access */
+	if (!l2cap_frame_get_le16(frame, &mtu))
 		return false;
+	pn.mtu = mtu;

 	if (!l2cap_frame_get_u8(frame, &pn.max_retrans))
 		return false;
--
2.8.0.rc3.226.g39d4020