[PATCH 2/3] usb-storage: alauda: check the return value of alauda_read_map()

[Arka Mondal <arka@arkamondal.net>]

alauda_ensure_map_for_zone() ignores the value alauda_read_map()
returns. On failure lba_to_pba[zone] and pba_to_lba[zone] are left NULL,
and both callers dereference them immediately:

  pba = MEDIA_INFO(us).lba_to_pba[zone][lba_offset];

alauda_read_map() returns USB_STOR_TRANSPORT_ERROR when either kcalloc()
fails or an alauda_get_redu_data() transfer fails, so one failed bulk
transfer is enough to reach the NULL dereference.

Return that value from alauda_ensure_map_for_zone() and check it in
alauda_read_data() and alauda_write_lba().

Fixes: e80b0fade09e ("[PATCH] USB Storage: add alauda support")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217862
Signed-off-by: Arka Mondal <arka@arkamondal.net>
---
 drivers/usb/storage/alauda.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/storage/alauda.c b/drivers/usb/storage/alauda.c
index 878c404106c5..d47ce01d519a 100644
--- a/drivers/usb/storage/alauda.c
+++ b/drivers/usb/storage/alauda.c
@@ -697,11 +697,13 @@ static int alauda_read_map(struct us_data *us, unsigned int zone)
  * Checks to see whether we have already mapped a certain zone
  * If we haven't, the map is generated
  */
-static void alauda_ensure_map_for_zone(struct us_data *us, unsigned int zone)
+static int alauda_ensure_map_for_zone(struct us_data *us, unsigned int zone)
 {
 	if (MEDIA_INFO(us).lba_to_pba[zone] == NULL
 		|| MEDIA_INFO(us).pba_to_lba[zone] == NULL)
-		alauda_read_map(us, zone);
+		return alauda_read_map(us, zone);
+
+	return 0;
 }
 
 /*
@@ -849,7 +851,9 @@ static int alauda_write_lba(struct us_data *us, u16 lba,
 	unsigned int new_pba_offset;
 	unsigned int zone = lba / uzonesize;
 
-	alauda_ensure_map_for_zone(us, zone);
+	result = alauda_ensure_map_for_zone(us, zone);
+	if (result != USB_STOR_TRANSPORT_GOOD)
+		return result;
 
 	pba = MEDIA_INFO(us).lba_to_pba[zone][lba_offset];
 	if (pba == 1) {
@@ -980,7 +984,10 @@ static int alauda_read_data(struct us_data *us, unsigned long address,
 		unsigned int lba_offset = lba - (zone * uzonesize);
 		unsigned int pages;
 		u16 pba;
-		alauda_ensure_map_for_zone(us, zone);
+
+		result = alauda_ensure_map_for_zone(us, zone);
+		if (result != USB_STOR_TRANSPORT_GOOD)
+			break;
 
 		/* Not overflowing capacity? */
 		if (lba >= max_lba) {
-- 
2.55.0