Re: [PATCH] sd: close hole in > 2T device rejection when !CONFIG_LBDAF

[Steve Magnani]

On 02/27/2017 12:57 PM, Bart Van Assche wrote:
...
How about the (untested) patch below? The approach below avoids that the check 
is
duplicated and - at least in my opinion - results in code that is easier to 
read.
I find lba_too_large() a little dense, but functionally OK. The "shift 
>= 0" clause could be dropped.
I tested this on my "problem" system (READ CAPACITY(10)) without incident.

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index cb6e68dd6df0..3533d1e46bde 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2082,6 +2082,16 @@ static void read_capacity_error(struct scsi_disk *sdkp, 
struct scsi_device *sdp,
        sdkp->capacity = 0; /* unknown mapped to zero - as usual */
  }
  
+/*
+ * Check whether or not logical_to_sectors(sdp, lba) will overflow.
+ */
+static bool lba_too_large(u64 lba, u32 logical_block_size)
+{
+       int shift = sizeof(sector_t) * 8 + 9 - ilog2(logical_block_size);
+
+       return shift >= 0 && shift < 64 && lba >= (1ULL << shift);
+}
+
  #define RC16_LEN 32
  #if RC16_LEN > SD_BUF_SIZE
  #error RC16_LEN must not be more than SD_BUF_SIZE
@@ -2154,7 +2164,7 @@ static int read_capacity_16(struct scsi_disk *sdkp, 
struct scsi_device *sdp,
                return -ENODEV;
        }
  
-	if ((sizeof(sdkp->capacity) == 4) && (lba >= 0xffffffffULL)) {
+       if (lba_too_large(lba + 1, sector_size)) {
                sd_printk(KERN_ERR, sdkp, "Too big for this kernel. Use a "
                        "kernel compiled with support for large block "
                        "devices.\n");
@@ -2243,7 +2253,7 @@ static int read_capacity_10(struct scsi_disk *sdkp, 
struct scsi_device *sdp,
                return sector_size;
        }
  
-	if ((sizeof(sdkp->capacity) == 4) && (lba == 0xffffffff)) {
+       if (lba_too_large(lba + 1ULL, sector_size)) {
                sd_printk(KERN_ERR, sdkp, "Too big for this kernel. Use a "
                        "kernel compiled with support for large block "
                        "devices.\n");