[PATCH 3.16 140/178] scsi: sd: Fix capacity calculation with 32-bit sector_t

[Ben Hutchings]

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>

commit 7c856152cb92f8eee2df29ef325a1b1f43161aff upstream.

We previously made sure that the reported disk capacity was less than
0xffffffff blocks when the kernel was not compiled with large sector_t
support (CONFIG_LBDAF). However, this check assumed that the capacity
was reported in units of 512 bytes.

Add a sanity check function to ensure that we only enable disks if the
entire reported capacity can be expressed in terms of sector_t.

Reported-by: Steve Magnani <steve.magnani@xxxxxxxxxxxxxxx>
Cc: Bart Van Assche <Bart.VanAssche@xxxxxxxxxxx>
Reviewed-by: Bart Van Assche <Bart.VanAssche@xxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/scsi/sd.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1930,6 +1930,22 @@ static void read_capacity_error(struct s
 
 #define READ_CAPACITY_RETRIES_ON_RESET	10
 
+/*
+ * Ensure that we don't overflow sector_t when CONFIG_LBDAF is not set
+ * and the reported logical block size is bigger than 512 bytes. Note
+ * that last_sector is a u64 and therefore logical_to_sectors() is not
+ * applicable.
+ */
+static bool sd_addressable_capacity(u64 lba, unsigned int sector_size)
+{
+	u64 last_sector = (lba + 1ULL) << (ilog2(sector_size) - 9);
+
+	if (sizeof(sector_t) == 4 && last_sector > U32_MAX)
+		return false;
+
+	return true;
+}
+
 static int read_capacity_16(struct scsi_disk *sdkp, struct scsi_device *sdp,
 						unsigned char *buffer)
 {
@@ -1995,7 +2011,7 @@ static int read_capacity_16(struct scsi_
 		return -ENODEV;
 	}
 
-	if ((sizeof(sdkp->capacity) == 4) && (lba >= 0xffffffffULL)) {
+	if (!sd_addressable_capacity(lba, sector_size)) {
 		sd_printk(KERN_ERR, sdkp, "Too big for this kernel. Use a "
 			"kernel compiled with support for large block "
 			"devices.\n");
@@ -2081,7 +2097,7 @@ static int read_capacity_10(struct scsi_
 		return sector_size;
 	}
 
-	if ((sizeof(sdkp->capacity) == 4) && (lba == 0xffffffff)) {
+	if (!sd_addressable_capacity(lba, sector_size)) {
 		sd_printk(KERN_ERR, sdkp, "Too big for this kernel. Use a "
 			"kernel compiled with support for large block "
 			"devices.\n");